<PAGE>   1
                                       
                                 UNITED STATES
                      SECURITIES AND EXCHANGE COMMISSION
                            Washington, D.C. 20549
                                       
                                   FORM 10-K
(X)   ANNUAL REPORT PURSUANT TO SECTION 13 OR 15(D) OF THE SECURITIES EXCHANGE
              ACT OF 1934 FOR THE FISCAL YEAR ENDED JUNE 30, 1995
                                       
                                      OR
                                       
  (  )   TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(D) OF THE SECURITIES
                             EXCHANGE ACT OF 1934
                                       
Commission file number 0-17999
                       --------
                
                               IMMUNOGEN, INC.
          -------------------------------------------------------
           (Exact name of registrant as specified in its charter)
                                       
        Massachusetts                                   04-2726691
  --------------------------------        ------------------------------------
   State or other jurisdiction of         (I.R.S. Employer Identification No.)
   incorporation or organization)

                    128 Sidney Street, Cambridge, MA  02139
        --------------------------------------------------------------
         (Address of principal executive offices, including zip code)
                                       
                                (617) 661-9312
            -----------------------------------------------------
             (Registrant's telephone number, including area code)
                                       
          Securities registered pursuant to Section 12(b) of the Act:
                                       
                                     None

          Securities registered pursuant to Section 12(g) of the Act:

                         Common Stock, $.01 par value
                               (Title of class)

Indicate by check mark whether the registrant (1) has filed all reports
required to be filed by Section 13 or 15(d) of the Securities Exchange Act of
1934 during the preceding 12 months (or for such shorter period that the
registrant was required to file such reports,) and (2) has been subject to such
filing requirements for the past 90 days.    Yes X   No
                                                 -

Aggregate market value, based upon the closing sale price of the shares as
reported by the Nasdaq National Market System, of voting stock held by
non-affiliates at September 18, 1995: $50,754,868 (excludes shares held by
Executive Officers, Directors, and beneficial owners of more than 10% of the
Company's Common Stock).  Exclusion of shares held by any person should not be
construed to indicate that such person possesses the power, direct or indirect,
to direct or cause the direction of management or policies of the registrant,
or that such person is controlled by or under common control with the
registrant.  Common Stock outstanding at September 18, 1995: 12,586,606 shares.

Indicate by check mark if disclosure of delinquent filers pursuant to Item 405
of Regulation S-K is not contained herein, and will not be contained, to the
best of registrant's knowledge, in definitive proxy or information statements
incorporated by reference in Part III of this Form 10-K or any amendment to
this Form 10-K.  [  ]


<PAGE>   2


DOCUMENTS INCORPORATED BY REFERENCE

Portions of the Registrant's Definitive Proxy Statement for its 1995 Annual
Meeting of Shareholders are incorporated by reference into Part III of this
Report.




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<PAGE>   3



PART I


ITEM I.  BUSINESS

ImmunoGen, Inc. ("ImmunoGen" or "the Company") develops pharmaceuticals,
primarily for the treatment of cancer.  The Company's products are
"immunoconjugates," each comprising a potent effector molecule -- a proprietary
toxin or drug -- coupled to a monoclonal antibody for delivery to and
destruction of targeted cells.  Through its subsidiary, Apoptosis Technology,
Inc. ("ATI") established in 1993, the Company is developing additional
technology platforms, based on the regulation of cell proliferation and
programmed cell death, or apoptosis, with which to identify therapeutic product
candidates for the treatment of cancer and viral diseases.

Since its inception, the Company has acquired significant expertise and
proprietary know-how with regard to the development of immunoconjugates for the
treatment of cancer.  The key elements of the Company's proprietary position
include its expertise in identifying and designing both potent effector
molecules and specific targeting agents.  Through its network of collaborators,
advisors and consultants, the Company also has access to significant medical
expertise with regard to the treatment of cancer.  Through ATI, the Company has
established collaborative ties with leading academic researchers in the area of
apoptosis research and its applications to the treatment of cancer and viral
diseases.

The Company uses several different toxins and drugs in its immunoconjugates as
effector molecules with which to destroy target cells.  In each of the
Company's first four products -- the Oncolysins -- a proprietary derivative of
ricin, a powerful, naturally occurring plant toxin, is coupled to a targeting
monoclonal antibody.  In the Company's next group of products -- small-drug
immunoconjugates -- potent small-molecule drugs are conjugated to humanized
monoclonal antibodies.  ATI is basing its proprietary technology portfolio on
the development of molecular and cellular screening systems for the
identification of leads for therapeutic product candidates.

The Company began conducting clinical trials with the first of the Oncolysin
products in 1988.  That first product, Oncolysin B, is now being tested in
lymphoma patients in a large-scale, randomized Phase III clinical study.  The
Company's small-drug immunoconjugates are in the research and preclinical
phases of development: in April 1994, the Company successfully submitted an
Investigational New Drug Application ("IND") with the U.S. Food and Drug
Administration ("FDA") to begin human clinical testing of anti-B4-DC1, its
first small-drug immunoconjugate.

The Company's products will require significant additional investment and
laboratory and clinical testing, and regulatory approvals.  The Company is
seeking to commercialize its products through collaborations with established
pharmaceutical companies to support clinical testing and development and
manufacturing and for product sales and marketing.  The Company also may elect
in the future to establish a specialized sales force in the United States and
to serve international markets through foreign licensees.  There can be no
assurance, however, that the Company will be successful in developing or
commercializing its products.

IMMUNOCONJUGATE TECHNOLOGY

The Company has developed two classes of effector molecules whose distinct
characteristics have yielded products it believes are uniquely suited to the
treatment of different stages of cancer; namely, as initial therapy or to
reduce the residual cancer cells that often remain after initial therapy.

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In the Company's first four products, the Oncolysins, blocked ricin (a
derivative of ricin, a potent, naturally occurring plant toxin readily
available from castor beans) is linked to a monoclonal antibody to form an
immunoconjugate.  The Company's blocked-ricin immunoconjugates possess high
potency, specificity for target cells and, importantly, a mechanism of cell
killing -- disruption of protein synthesis -- that is not shared by
conventional anticancer agents.  The mechanism of action of blocked-ricin
immunoconjugates makes them particularly attractive agents for the treatment of
the subclinical (undetectable) residual disease which frequently remains after
initial chemotherapy.  Residual disease may be resistant to conventional agents
and often regrows, causing relapsed disease.

The Company has conducted in vitro tests which compare the potency of blocked
ricin to the most commonly used conventional chemotherapeutic agents, including
adriamycin, methotrexate, actinomycin D, vinblastine and mitomycin C.  In these
tests, the Company has shown that the same proportion of tumor cells is killed
by antibody immunoconjugates of blocked ricin at concentrations 1,000-times
lower than those of the chemotherapeutic drugs tested.  Thus, due to the
potency and specificity of the immunotoxin, blocked-ricin immunoconjugates have
the potential for greater tumor destruction before reaching dose levels which
cause severe illness or death in the patient.

ImmunoGen believes it is the only company with a proprietary position in an
effective derivative of intact ricin.  See "Patents, Trade Secrets and
Trademarks."  Two U.S. patents relating to blocked ricin and its use in
antibody conjugates have issued to Dana-Farber Cancer Institute
("Dana-Farber"): No. 5,239,062, issued in August 1993, and No. 5,395,924,
issued in March 1995.  ImmunoGen has an exclusive worldwide license for all
therapeutic applications of these patents.

The Company has also tested two groups of small-molecule drugs, each as toxic
as ricin, which it believes offer great promise for use as effector molecules
in immunoconjugates.  The Company has developed derivatives of these drugs
which allow them to be attached to antibodies to target tumor cells and allow
for their release at the target site in a fully active form.

The first compound, DC1, is representative of a group of agents called natural
groove-binding compounds.  After binding to DNA, these agents attach
covalently, thereby interfering with cellular function and inducing the death
of cells.  ImmunoGen has incorporated DC1 into several immunoconjugates, and in
April 1994 the Company submitted an IND to FDA to begin human testing of its
first DC1-based immunoconjugate.  In June 1995, the Company received a $750,000
Phase II Small Business Innovation Research ("SBIR") grant from the National
Cancer Institute ("NCI") of the National Institutes of Health to help fund
development of DC1-based immunoconjugates.  The award is for $375,000 annually
for two years beginning June 1, 1995.  In August 1995, the Company received
notification from the U.S. Patent and Trademark Office that a U.S. patent will
soon issue on the use of DC1 in immunoconjugates.

The second small-drug compound, DM1, binds to tubulin and is a potent inhibitor
of cell division.  It is derived from maytansine, a natural product.  The
Company has obtained an exclusive license for use of maytansine in conjugated
form.  See "Licenses -- Takeda Chemical Industries Ltd."  The Company has
received two patents, No. 5,208,020, issued in May 1993, and No. 5,416,064,
issued in May 1995, covering the use in conjugated form of small-drug
immunoconjugates derived from maytansine.

The Company has conducted IN VITRO tests that it believes demonstrate that
immunoconjugates containing either DC1 or DM1 are more effective than current
anticancer drugs at killing tumor cells.  This high degree of killing power is
important in debulking tumor masses.  In animal tumor models using SCID 

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mice, small-drug immunoconjugates have shown therapeutic efficacy and complete
cures at low doses with no toxicity to normal tissues.  In September 1995,
the Company published the results of its in vitro and animal studies of
DC1-based immunoconjugates in a leading medical journal, Cancer Research.

The specificity of an antibody forms the basis for its use to deliver effector
molecules to disease sites.  Antibodies are proteins produced by the immune
system in response to the presence of foreign substances in the body.  A
particular antibody detects and binds to only one specific antigen, or marker.
Since cancer cells may have unique antigens on their surfaces, an antibody with
the correct specificity for those cells may be used as a targeting agent.  When
such an antibody is coupled to a highly toxic agent, forming an
immunoconjugate, tumor cells are killed while normal cells, even those in close
association with the tumor, can be spared.

The Company uses humanized monoclonal antibodies as targeting agents in its
small-drug immunoconjugates because they are expected to be nonimmunogenic.
Nonimmunogenic molecules are desirable because, over time, a patient's immune
system may recognize a nonhuman protein as foreign and remove it from
circulation.  As a result, the triggering of an immune response may limit the
ability to conduct long-term therapy using immunoconjugates comprising nonhuman
proteins.  Because they are expected to be nonimmunogenic, the Company's
small-drug immunoconjugates are being developed for long-term dosing for the
treatment of patients who have relapsed and for debulking tumor masses.

ImmunoGen has invested in two antibody humanization techniques for the
development of these nonimmunogenic targeting agents for use in its small-drug
immunoconjugates: CDR grafting and resurfacing.  The Company has humanized the
antibodies used in Oncolysin B and Oncolysin S using both CDR grafting and
resurfacing -- techniques that alter antibodies derived from animals to make
them appear human to the immune system.  Laboratory experiments have
demonstrated that these humanized antibodies maintain the same level of
high-affinity binding as the original, mouse-derived antibodies.  In addition
to these, the Company intends to humanize other antibodies, including those
which target solid tumors.  In February 1995, the Company entered into an
agreement with Oxford Molecular Ltd ("OML"), a research and development firm
which provides computer software for modeling protein structure, under which
OML receives rights to utilize the Company's antibody resurfacing technology.
See "Licenses -- Oxford Molecular Ltd."

APOPTOSIS TECHNOLOGY

In January 1993, the Company established ATI, a subsidiary founded to develop
screening systems for drugs which influence the regulation of cell
proliferation and programmed cell death, or apoptosis.  Initially, ATI licensed
technology from Dana-Farber.  See "Licenses -- Dana-Farber Cancer Institute."
ATI's strategy has been to leverage existing knowledge in the field of
apoptosis by developing, at the discovery stage, a series of key research
collaborations with academic scientists.  To this end, in addition to its
collaboration with Dana-Farber in this area, ATI has established collaborative
ties with leading scientists at additional academic centers to complement its
own internal research team.

ATI is expected to identify leads for the development of therapeutic product
candidates based on the regulation of cell proliferation and apoptosis, the
natural, orderly process by which cells in the body die or are killed.  The
Company expects that, over the next several years, research at ATI will yield a
flow of new product candidates which ImmunoGen, under the terms of its
agreement with ATI, will have the option to commercialize.  For the past two
years, ATI has been engaged in the identification of specific diseases which
may be treated through the regulation of apoptosis and is focusing its efforts
on cancer and viral diseases.

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<PAGE>   6

Apoptosis is an active process regulated by specific genes.  All cells have the
potential to undergo apoptosis.  The activation of a cell death program is
regulated by a multitude of signals that either can originate on the cell
surface and be transmitted through receptors to intracellular pathways, or
which arise in the interior of the cell.  The discovery over the past few years
of key regulatory elements makes it possible to develop novel therapies
intended to enhance or decrease the tendency of specific cell populations to
undergo apoptosis.

ATI's research objective is to define opportunities for intervention at key
signaling points in these pathways.  Because of promising research developments
made both at ATI and in the laboratories of its collaborators in the regulation
of so-called "ANTI-DEATH" genes and SURVIVAL SIGNALS, ATI has focused its 
discovery efforts on the identification of molecular targets and the subsequent
development of molecular screening systems in these areas.

REGULATION OF ANTI-DEATH GENES. Tumor cells escape apoptosis through the active
suppression of stimuli which directly induce apoptosis.  For example, the BCL-2
proto-oncogene can block cell death induced by a broad spectrum of
apoptosis-inducing stimuli.  Therefore, it has been categorized as a regulator
of cell death, or an "anti-death" gene.  It is known that BCL-2 is a member of
a small gene family and that interactions among the members of this family may
regulate its function.

In April 1995, ATI researchers published the results of cloning and functional
analysis of Bak, a member of the BCL-2 gene family which, unlike BCL-2,
promotes cell death.  Laboratory experiments have shown that forced expression
of Bak induces rapid and extensive apoptosis, raising the possibility that it
is directly involved in the machinery of a cell death program.  Further, ATI
scientists have identified the domain in Bak that ATI believes is both
necessary and sufficient to trigger cell-killing activity.  This domain gives
ATI a molecular target with which to begin the design of screens for drugs
which trigger apoptosis.

ATI is pursuing ways of disrupting the suppression of Bak function by Bcl-2
family members.  In addition, ATI, with outside collaborators at the St. Louis
University Medical Center, have demonstrated that Bak is the target of
inhibitory gene products from two unrelated viruses and are now progressing
toward identification of the anti-apoptotic mechanisms of cytomegalovirus.

REGULATION OF THE CELL DEATH PATHWAY BY SURVIVAL SIGNALS.  In normal, healthy
tissue, proliferation and cell death are coupled, providing an efficient means
for organisms to control unwanted or excess cellular proliferation.  However,
cancer cells have accumulated mutations that circumvent the normal regulation
of proliferation and cell death, leading to excess and uncontrolled cell growth
not compensated for by apoptosis.  One way that the cell suppresses the cell
death program is through mediation of survival signals provided by growth
factors such as insulin-like growth factor 1 ("IGF-1").  Research from the
laboratory of Dr. Gerard Evan of the Imperial Cancer Research Fund ("ICRF"), a
leading cancer research foundation in the United Kingdom, has shown that
survival signals provided by IGF-1 help prevent cells transformed by the MYC
proto-oncogene from undergoing apoptosis.  ATI has established a research
program with Dr. Evan to dissect the role of IGF-1 and other survival factors
in the death pathway and to identify drugs that mimic or disrupt the survival
signal of IGF-1 in cells.  See "Licenses -- Imperial Cancer Research Fund."
Since the IGF-1 receptor ("IGF-1R") is overexpressed on cells of many tumor
types, such as breast and small-cell lung carcinoma, it is expected that the
down-regulation of survival signals should induce apoptosis in a great number
of tumor types, potentially offering ATI highly specific therapeutics for an
array of cancers.


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<PAGE>   7
To further enhance this program, in January 1995, ATI signed a consulting
agreement with Dr. Renato Baserga of Thomas Jefferson University, Philadelphia,
Pennsylvania, an expert on IGF-1R and its role in proliferation, transformation
and regulation of apoptosis.  Dr. Baserga and his laboratory have provided ATI
with IGF-1R mutants with which to study ways of intervening with the IGF-1
survival signal and thereby triggering the cell death program.  In
collaboration with Dr. Baserga, ATI has identified areas on IGF-1R which are
necessary to transmit the survival signal, thereby providing potential
molecular targets for drug design.

PRODUCTS

ImmunoGen has selected specific markets in which to focus its initial product
development efforts.  Oncolysin B and Oncolysin M are designed to treat
patients in remission with lethal forms of blood-cell malignancies.  Oncolysin
S is an immunoconjugate for the treatment of small-cell lung cancer ("SCLC")
patients in remission and Oncolysin CD6 is designed for the treatment of T-cell
malignancies in remission and for acute organ transplant rejection.  The
Company's small-drug immunoconjugates are being developed as initial therapy
for lymphoma, SCLC and certain solid tumors.  The Company believes that
applications of the Oncolysin products, to treat patients in remission to
prevent or substantially delay relapse, will be complementary to those of its
small-drug immunoconjugates, which are being developed for use as initial
therapy and as agents for long-term administration.

In December 1994, the Company implemented a restructuring which included the
suspension of operations at its Canton and Norwood production facilities and
the reduction or elimination of certain areas of the Company's research.  This
plan resulted in the termination of approximately 100 employees, or an
approximately 60% reduction in workforce.  As part of the restructuring, the
Company focused its clinical resources on Oncolysin B and scaled back clinical
trials of its other products.  Clinical development of the other Oncolysins -
including Oncolysin S, which has progressed into Phase II testing for the
treatment of small-cell lung cancer - is expected to remain on hold until the
Company enters into new agreements with third parties to support their
commercialization.  The Company's small-drug immunoconjugates, now in the
research and preclinical stages of development, also will not enter human
clinical trials until third-party funding is secured for them.

The Company expects that future expenditures for manufacturing improvements and
for new clinical trials will be defrayed by corporate partners.  Although the
Company currently is seeking such partners, no such arrangements have been
concluded nor is there any assurance that any such arrangements may be
concluded.

The following table summarizes the current development status of the Company's
products and product candidates.  For a description of Phase I-III clinical
trials, see "Regulatory Issues -- Clinical Trials Process." Preclinical denotes
work to refine product performance characteristics and studies relating to
product composition, stability, scale-up, toxicity and efficacy to create a
prototype formulation in preparation for submission of an IND application to
FDA to begin human clinical studies.  Research denotes work up to and including
bench-scale production of a formulation which meets the basic product
performance characteristics established for the product.  For products now in
clinical testing, each line item in the table represents a separate clinical
indication:

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<TABLE>
DEVELOPMENT STATUS OF IMMUNOGEN'S PRODUCTS

<CAPTION>
Product/Application             Clinical Setting                        Status
<S>                             <C>                                     <C>
I.  ONGOING DEVELOPMENT:
Oncolysin B
  B-Cell Lymphomas              After Autologous Bone Marrow            Phase III
  and Leukemias                   Transplantation (1)
                                AIDS-Related Lymphoma (2)               Phase I/II
                                Synergy with Chemotherapy               Phase I/II
                                Pediatric                               Phase I (NCI IND)

Anti-B4-DC1
  B-Cell Lymphomas              Tumor Debulking                         IND Accepted

huN901-DC1
  Small-Cell Lung Cancer        Tumor Debulking                         Preclinical

Colon-DM1
  Colon Cancer                  Tumor Debulking                         Research

Anti-EGFR-DM1
  Squamous-Cell Carcinomas      Tumor Debulking                         Research

II.  SUSPENDED, CLOSED OR COMPLETED CLINICAL STUDIES:
Oncolysin B
  B-Cell Lymphomas              After Chemotherapy (2,3)                Phase II
  and Leukemias                 At Relapse (3)                          Phase I/II
                                Bone Marrow Purging (3)                 Phase I/II

Oncolysin S
  Small-Cell Lung Cancer        After Chemotherapy (4)                  Phase II
  CD56+ Pediatric Tumors        At Relapse                              Phase I (NCI IND)

Oncolysin M
  Myelogenous Leukemias         Bone Marrow Purging (3)                 Phase I/II

Oncolysin CD6
  T-Cell Cancers                After Relapse (4)                       Phase I
<FN>
(1)Pivotal study to serve as the basis for Product License Application ("PLA").
(2)Studies to generate data to support Oncolysin B PLA.
(3)Study closed; no new trials planned in this clinical setting.
(4)Not currently enrolling patients to focus additional clinical resources to
   Oncolysin B PLA.
</TABLE>


With certain exceptions, ImmunoGen has conducted its own clinical studies.  The
ongoing Phase III trial of Oncolysin B is being conducted in conjunction with
the Cancer and Leukemia Group B ("CALGB") and the Eastern Cooperative Oncology
Group ("ECOG"), both NCI cooperative groups.  Currently, the 

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study is open to enrollment at 42 sites in the United States and Canada. 
The Company also supports some clinical trials of the Oncolysin products which
are conducted directly by the NCI.

Oncolysin B.  Non-Hodgkin's lymphoma affects an estimated 45,000 new patients
every year in the United States; over 36,000 suffer from the B-cell variant.
There are approximately 19,000 deaths each year among B-cell lymphoma patients.
There are also approximately 12,500 new cases of acute and chronic lymphocytic
leukemia in the United States each year.  Approximately 5,700 persons die of
these B-cell leukemias annually, the majority of whom are under the age of
twenty.  Oncolysin B uses an antibody, anti-B4, to target blocked ricin
specifically to a marker, CD19, found on these B-cell malignancies.

As indicated in the preceding table, Oncolysin B is being evaluated for a
number of different indications and in a number of different settings.  Over
800 patients have been enrolled in clinical studies of Oncolysin B using the
drug intravenously or as a bone marrow purging agent.  Clinical responses have
been observed in these trials with an acceptable side-effect profile.

Based on encouraging data from Phase I and Phase II studies in patients with
minimal residual disease, the Company began enrollment of patients in a
pivotal, multicenter Phase III study of Oncolysin B in July 1993.  This study
is measuring the effectiveness of the drug in the treatment of relapsed
lymphoma patients subsequent to autologous bone marrow transplantation
("ABMT").  In the ABMT procedure, a portion of the patient's bone marrow is
removed and stored and a remission is then induced with high-dose chemotherapy,
with or without radiation.  This intensive chemotherapy and radiation
obliterates the remaining bone marrow and the patient is then salvaged by
reinfusion of the previously stored marrow.  Even if these patients have no
clinical evidence of disease subsequent to ABMT, 50-70% are expected to relapse
in two years because of occult, residual tumor.

The Company believes that the ABMT setting, which numbers approximately 5,000
new cases per year in the United States, serves as a model for all B-cell
malignancy patients in remission.  The Phase III trial measures the time to
relapse of patients in complete remission who receive Oncolysin B subsequent to
ABMT versus results for those who do not receive the drug subsequent to ABMT.

Enrollment in the Oncolysin B Phase III trial was slower than anticipated in
1995.  The Company expects enrollment in the trial to continue at least through
1996 and does not expect to submit data to FDA until 1998, at the earliest.  A
number of factors make the time to completion of the Phase III trial difficult
to predict.  These include the rate of enrollment of patients into the trial,
the number of patients who are declared ineligible or who voluntarily drop out
prior to randomization (the time when patients are divided into two groups --
treatment with Oncolysin B versus observation) and their time to relapse
subsequent to randomization.

The Company also has tested Oncolysin B in Phase II trials in patients who are
in remission following conventional chemotherapy.  Unlike patients in the
ongoing Phase III study, these patients did not undergo ABMT.  Using supportive
data from these studies, the Company intends to seek approval to use Oncolysin
B to treat the entire population of patients with B-cell malignancies who are
in remission (or who have minimal residual disease), no matter how the
remission has been achieved.

AIDS-related lymphoma is another setting where the Company believes Oncolysin B
may be effective.  Two Phase I studies of Oncolysin B began in this setting in
the fall of 1991, one of which was performed under an IND submitted by NCI.
AIDS-related lymphoma is a devastating disease where conventional chemotherapy
has limited effectiveness and relapsed disease usually is refractory to
additional 

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chemotherapy.  A further problem in the treatment of AIDS-related
lymphoma is that the aggressive chemotherapy normally undertaken for lymphoma
patients may not be tolerated by patients with AIDS. Because Oncolysin B does
not suppress the bone marrow, the Company believes that AIDS patients with
compromised bone marrow function may tolerate Oncolysin B better than they
tolerate the myelosuppressive agents normally used to treat lymphoma.

Forty patients were treated in the initial Phase I/II trials in AIDS-related
lymphoma, and preliminary data indicate that Oncolysin B may be given safely to
these patients.  The data also suggest that Oncolysin B may cause significant
tumor shrinkage in relapsed patients.  Based on these results, in September
1994 the Company initiated a Phase I/II trial of patients given combination
conventional chemotherapy and a 28-day continuous infusion of Oncolysin B.
This study met its objectives and was completed in September 1995.

Encouraging laboratory and preclinical results also led the Company to begin a
Phase I/II trial of Oncolysin B using the drug in combination with conventional
agents.  Studies in mice which had been given B-cell tumors show that combining
Oncolysin B with the conventional chemotherapeutics adriamycin or vincristine
produced additive, or synergistic, anti-tumor effects -- superior to those seen
with Oncolysin B or the conventional agents alone.  Furthermore, ImmunoGen
scientists observed enhanced cell killing using Oncolysin B in combination with
the conventional agents on tumors which were resistant to conventional drugs.
The Phase I/II study testing the synergistic effects of Oncolysin B in
combination with conventional chemotherapy began in September 1994 in lymphoma
patients and is ongoing.

Oncolysin S.  Lung cancer is diagnosed in over 172,000 Americans every year and
their overall five-year survival rate is approximately 13%.  However, over 30%
of these patients (approximately 55,000 per year) have small-cell lung cancer
("SCLC") and their five-year survival rate is only 1%.  Using the N901
antibody, which binds to an antigen, CD56, found on SCLC, the Company initiated
a clinical trial with Oncolysin S in early 1991.

The Company completed its initial Phase I study of Oncolysin S in March 1993.
The trial established that the drug may be administered safely, is well
tolerated and is delivered to the tumor.  Clinicians also saw one partial
response and observed stabilization of disease in six other patients treated in
the trial.  The Company believes these results are very encouraging, especially
since current therapies for relapsed SCLC rarely produce durable responses and
the long-term prognosis for these patients is poor.

Based on the results obtained in the initial study, the Company initiated a
Phase II trial in September 1993 in patients with a best response following
conventional chemotherapy.  Following treatment with Oncolysin S, a subset of
patients developed abnormalities which could be consistent with interaction of
the N901 antibody with cardiac tissues.  The Company stopped enrollment of new
patients in Oncolysin S trials in October 1994, before treating a sufficient
number of patients to be able to make an assessment of responses or of
potential cross-reactivity of the antibody in this patient group.  The Company
cannot estimate the time to completion of the Phase II trial, nor does it
intend to expand into additional Phase II trials of Oncolysin S, due to the
focus of its clinical effort on studies of Oncolysin B to support its first
Product License Application ("PLA"), until it secures third-party support.

Oncolysin M.  Acute myelogenous leukemia affects approximately 12,000 new
patients annually in the United States; approximately 7,500 patients die of the
disease each year.  Anti-My9 is a highly specific antibody for these leukemia
cells which, when combined with the Company's blocked ricin, yields a potent
immunoconjugate.


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Early results of bone marrow purging studies indicate that Oncolysin M
decreases the number of malignant cells while not damaging the stem cells
necessary for successful regrowth of the marrow.  The study achieved its
objectives and the Company does not plan to initiate new trials of Oncolysin M
until it secures third-party support.

Oncolysin CD6.  ImmunoGen has developed Oncolysin CD6, a product which may have
applications in the inhibition of the inflammatory response, mediated by T
cells, which accompanies autoimmune disease.  An IND for Oncolysin CD6 was
submitted to FDA in February 1992 seeking to test the ability of the drug to
suppress the immune system and prevent rejection of organ transplants.  In
response, FDA requested that the first clinical test of Oncolysin CD6 be
conducted in a population of patients with life-threatening illness.  The
Company then prepared an IND amendment to evaluate Oncolysin CD6 in patients
with cutaneous T-cell lymphoma or leukemia.  The Company began a Phase I study
in this setting in June 1993, which has been placed on hold by the Company in
order to permit the Company to focus its clinical effort on studies of
Oncolysin B to support its first PLA.  The Company cannot estimate the time to
completion of the Phase I trial, nor does it intend to expand trials of
Oncolysin CD6 until it secures third-party support.

Anti-B4-DC1.  The first of the Company's small-drug immunoconjugates,
anti-B4-DC1 consists of the same antibody as in Oncolysin B (anti-B4) linked to
the potent small-drug effector molecule, DC1.  DC1 is a synthetic drug and is
not expected to be immunogenic.  The immunoconjugate, therefore, may be a
suitable agent for tumor debulking.  The Company submitted an IND to begin
testing anti-B4-DC1 in relapsed lymphoma patients in April 1994.  The FDA has
accepted its application and the Company expects to initiate human clinical
trials when it enters into an agreement with a corporate partner to support
commercialization.

huN901-DC1.  This product consists of a humanized version of the antibody in
Oncolysin S (N901), conjugated to DC1.  The antibody has been humanized
successfully, and the Company has expressed it in cells at sufficiently high
levels to begin manufacturing scale up.  As with anti-B4-DC1, the Company will
not begin clinical testing of huN901-DC1 before a corporate partner is found to
support further development and commercialization.  The Company expects to test
huN901 as a tumor debulking agent in small-cell lung cancer.

Colon-DM1.  Under a research agreement with a major pharmaceutical company, the
Company has been testing an antibody which targets colon cancer cells.  The
Company believes this antibody possesses the requisite specificity which would
make it a useful targeting agent in a small-drug immunoconjugate: the antibody
binds strongly to 70% of colon cancers and has minimal cross-reactivity with
normal human tissues.  Upon the successful execution of a licensing agreement
to obtain commercial rights to the antibody, the Company expects to humanize
it, conjugate it to DM1 and begin preclinical studies.  The Company will not
begin clinical testing of colon-DM1 until a corporate partner is found to
support clinical development and commercialization.

Anti-EGFR-DM1.  The Company currently is evaluating several new antibodies,
developed at ImmunoGen, which are directed against the epidermal growth factor
receptor ("EGFR").  EGFR is overexpressed on many solid tumors, such as head
and neck cancer and non-small-cell lung cancer.  The Company will not pursue
further development of this immunoconjugate until it secures third-party
support.



                                     11

<PAGE>   12

BUSINESS STRATEGY

ImmunoGen's products may be marketed potentially by licensees or by the
Company.  The Company recognizes that successful marketing of its anticancer
products both in the United States and abroad will require resources and
expertise not resident in-house and may be beyond the capabilities of all but
the largest pharmaceutical marketing organizations.  The Company therefore is
seeking marketing agreements or other exchanges of product rights with
established pharmaceutical companies in order to reach the oncology community.
ImmunoGen's strategy is to license rights to its products and require that its
licensees fund the Company's later-stage development work on its products.  The
Company may also, in the future, develop a small sales force to introduce and
detail its products; however, it has no current plans to do so.

To reduce expenditures and focus on its competitive strengths in research and
preclinical product development, the Company implemented a restructuring in
December 1994 which included a 60% reduction in its workforce.  The Company
believes that it has already produced sufficient quantities of its products to
support ongoing clinical trials, and the restructuring included the suspension
of manufacturing.  The Company expects that future expenditures for
manufacturing improvements, as well as for new clinical trials, will be
defrayed by corporate partners.

LICENSES -- IMMUNOGEN, INC.

Dana-Farber Cancer Institute.  Under the Company's Research and License
Agreement with Dana-Farber, entered into in May 1981, the Company has provided
funds for research projects conducted by Dana-Farber involving the development
of monoclonal antibodies, toxins and drugs for conjugation and use as cancer
therapeutics.  Dana-Farber retains ownership of the technology developed
through such research and has granted the Company a worldwide exclusive license
to use such technology in the Company's products, including the right to
sublicense to others.  The Company's first four products, Oncolysin B,
Oncolysin M, Oncolysin S and Oncolysin CD6, and several of the Company's other
products under development, use Dana-Farber technology which has been licensed
to the Company under this agreement.

In return for these rights, the Company has agreed to pay Dana-Farber royalties
on product sales by ImmunoGen and its sublicensees.  In general, royalties on
sales by ImmunoGen of products based primarily on patented Dana-Farber
technology will be paid at the rate of 4% of ImmunoGen's net sales, and
royalties on products based primarily on unpatented Dana-Farber technology will
be paid at a reduced rate to be agreed upon.  ImmunoGen is required to pay to
Dana-Farber 20% of royalties that the Company receives from sublicensees on
sales by them of ImmunoGen's products based primarily on patented Dana-Farber
technology and a reduced percentage, to be agreed upon, with respect to
products based primarily on unpatented Dana-Farber technology.  As of August
1995, no royalties have been paid under the agreement.

The licenses of Dana-Farber technology and related royalty obligations continue
with respect to patented technology for the life of the related patent, and
with respect to unpatented technology until such technology becomes public (but
not longer than 17 years after first commercial sale).  The Dana-Farber
Research and License Agreement is automatically extended from year to year
unless terminated by either party on 60 days' prior written notice, but all
outstanding licenses and royalty obligations at the time of termination
continue.


                                     12

<PAGE>   13

Initial clinical trials of the Company's first three products have been
conducted principally at Dana-Farber.  Because of its reputation, Dana-Farber
attracts a large number of patients suffering from different forms of cancer.
Thus, the Company's long-standing relationship with Dana-Farber has permitted
ready access to a large pool of patients for clinical trials at one location
which might not otherwise be available to the Company.

Oxford Molecular Ltd.  In March 1995, the Company entered into an agreement
with OML under which the two companies cross-licensed technology for the design
of monoclonal antibodies.  Under the agreement, the Company receives access to
OML's molecular modeling software in exchange for granting OML the right to use
the Company's proprietary resurfacing technology in the development of
monoclonal antibodies outside of the field of oncology and case-by-case rights
within oncology areas not under development at the Company.  OML also will pay
the Company a percentage of the gross revenues it derives from the use of
resurfacing.

Takeda Chemical Industries, Ltd.  A licensing agreement with Takeda Chemical
Industries, Ltd. ("Takeda"), executed in April 1994, gives the Company a
worldwide license to make, use and market immunoconjugate products containing
maytansine or its analogs.  Under the agreement, Takeda will receive a royalty
of 4% of ImmunoGen's annual net sales of such products and will have a right of
first refusal to market such products in most Asian and certain Middle Eastern
countries.

In addition, Takeda will furnish to ImmunoGen, free of charge, up to 40 grams
of maytansine for research and development during the term of the license
agreement.  Subsequent supplies will either be furnished by Takeda on a cost
plus 15% basis or produced by ImmunoGen with royalties payable to Takeda equal
to 15% of ImmunoGen's cost.

LICENSES -- APOPTOSIS TECHNOLOGY, INC.

Dana-Farber Cancer Institute.  In January 1993, ATI and Dana-Farber entered
into a licensing agreement in the field of apoptosis under which ATI was
granted an exclusive, worldwide license, with full right to enter into
sublicense agreements, for all therapeutic applications and certain diagnostic
applications arising from existing inventions and an option to license future
inventions made in specified laboratories at Dana-Farber.  In consideration for
this license, Dana-Farber received a minority equity share in ATI, an initial
license fee and a commitment by ATI to fund the research activities of those
laboratories at Dana-Farber from which ATI is to derive rights under the
agreement.  Additionally, ATI will provide Dana-Farber milestone payments and
pay royalties based upon the sale of any products which incorporate licensed
Dana-Farber technology.  As of August 1995, no milestone or royalty payments
have been made under this agreement.

Imperial Cancer Research Fund and Imperial Cancer Research Technology Ltd.  In
July 1994, ATI entered into a three-year research and development collaboration
agreement in the field of apoptosis and cell proliferation with the Imperial
Cancer Research Fund ("ICRF") and the Imperial Cancer Research Technology Ltd
("ICRT"), ICRF's technology transfer arm, under which ATI was granted an
exclusive, worldwide license, with full right to enter into sublicense
agreements, for all therapeutic and diagnostic applications arising from
existing inventions and an option to license future inventions within the scope
of the collaboration made in specified laboratories at ICRF.  In consideration
for this license, ICRT received a minority equity interest in ATI in addition 
to a commitment by ATI to fund ongoing research in those ICRF laboratories from
which ATI will derive rights under the agreement.  ATI also will give ICRT
royalty payments on the sale of any products which incorporate licensed ICRF
technology.  As of August 1995, no milestone or royalty payments have been made
under this agreement.


                                     13

<PAGE>   14

PATENTS, TRADE SECRETS AND TRADEMARKS

ImmunoGen seeks patent protection for its proprietary technology and products
both in the United States and abroad.  Nine patents have been issued to
Dana-Farber in the United States covering technology exclusively licensed by
ImmunoGen, along with several patents in Canada, Europe and Japan.  Five of
these patents claim a variety of acid-labile and photo-labile conjugation
technologies as inventions; one claims a toxin immunoconjugate as an invention;
one claims a monoclonal antibody specific to small-cell lung carcinoma cells as
an invention; and two claim the use of blocked ricin in immunoconjugates.
Also, the Company has received two patents on the use of maytansinoids in
conjugated form.

Additional patent applications covering proprietary toxins, small-drug
derivatives, immunoconjugates and use of certain of these products for
indicated diseases have been submitted in the United States, Canada, Europe and
Japan and are pending or awaiting examination.  Work leading to other patent
applications is being performed by Company employees.  In all such cases, the
Company will either be the assignee or owner of such patents or have an
exclusive license to the technology covered by the patents.  No assurance can
be given, however, that the patent applications will issue as patents or that
any patents, if issued, will provide ImmunoGen with adequate protection against
competitors with respect to the covered products, technology or processes.

The Company is aware that a patent issued to a third party in Europe containing
claims covering the Company's blocked-ricin technology.  The Company also is
aware that patents have been issued in Australia and New Zealand, that a patent
application has been filed in Canada, and the Company believes that a patent
application has been filed in the United States, each of which contains claims
which may cover the Company's blocked-ricin technology.  The Company has
contested the European patent and that patent has now officially lapsed.  The
Company believes that the Australian and New Zealand patents are narrow and do
not encompass its blocked-ricin technology.  The Company may initiate
revocation proceedings against the Australian and New Zealand patents and
initiate interference proceedings against the Canadian and United States
applications if such patents are shown to cover the Company's blocked-ricin
technology.  The Company believes that, on the merits of its case, it will be
able to successfully challenge any of the above-listed potential competing
claims on its blocked-ricin technology.  There can be no assurance, however,
that the Company will be successful in any opposition, revocation or
interference proceeding.  Moreover, there can be no assurance that additional
patents containing similar claims will not be issued in other jurisdictions.

Many of the processes and much of the know-how of importance to the Company's
technology are dependent upon the skills, knowledge and experience of certain
of the Company's key scientific and technical personnel, which skills,
knowledge and experience are not patentable.  To protect its rights in these
areas, the Company requires all employees and most consultants, advisors and
collaborators to enter into confidentiality agreements with ImmunoGen.  There
can be no assurance, however, that these agreements will provide meaningful
protection for the Company's trade secrets, know-how or other proprietary
information in the event of any unauthorized use or disclosure of such trade
secrets, know-how or proprietary information.  Further, in the absence of
patent protection, the Company may be exposed to competitors who independently
develop substantially equivalent technology or otherwise gain access to the
Company's trade secrets, know-how or other proprietary information.



                                     14

<PAGE>   15

The Company has exclusive rights to a large number of antibodies, most of which
are covered by Dana-Farber patents or patent applications in the United States
and abroad.  In many cases, the underlying antigens also are patented.

The Company has also obtained a registered trademark -- Oncolysin(r) -- for its
first group of products.

COMPETITION

The areas of product development on which the Company has focused are highly
competitive.  ImmunoGen's competitors include major pharmaceutical and chemical
companies, specialized biotechnology firms, universities and research
institutions, many of which have greater resources than the Company.  In
addition, many specialized biotechnology firms have formed collaborations with
large, established companies to support research, development and
commercialization of products that may be competitive with those of the
Company.  Competitive factors within the cancer therapeutic market include the
safety and efficacy of products, the timing of regulatory approval and
commercial introduction, special regulatory designation of products, such as
Orphan Drug status, and the effectiveness of marketing and sales efforts.

The Company's competitive position also depends on its ability to attract and
retain qualified personnel, develop effective proprietary products, implement
production and marketing plans, obtain patent protection and secure sufficient
capital resources.

Competitors have developed products which currently are in clinical trials on
B-cell lymphoma, a disease for which the Company has designed Oncolysin B, its
first product.  The Company does not believe that any of these products are
being developed for the treatment of patients in remission with minimal
residual disease.  Competitors have initiated clinical trials of modified
monoclonal antibodies for the treatment of acute myelogenous leukemia, the
disease for which Oncolysin M has been designed.  Competitors also have begun
clinical trials of monoclonal antibody-based products for the treatment of
small-cell lung cancer which could compete with Oncolysin S, although none are
known by the Company to be directed at the treatment of minimal residual
disease.  The Company also is aware of competitors developing
monoclonal-antibody based products to purge cancer cells ex vivo, which may
compete with the ex vivo use of Oncolysin B or Oncolysin M or which may be used
to perfuse organs before transplant, and so may compete with the organ
transplant indication of Oncolysin CD6.

Technologies other than those involving monoclonal antibodies can be applied to
the treatment of cancer.  The application of recombinant DNA technology to
develop potential products made of proteins that occur normally in the body in
small amounts has been underway for some time.  Included in this group are
Interleukin-2, the interferons, tumor necrosis factor, colony stimulating
factors and a number of other biological response modifiers.  The Company
believes that these products offer only limited competition for ImmunoGen's
anticancer products.

Continuing development of conventional chemotherapeutics by large
pharmaceutical companies carries with it the potential for discovery of an
agent active against resistant forms of non-Hodgkin's lymphoma, acute and
chronic lymphocytic leukemia, acute myelogenous leukemia and small-cell lung    
cancer -- the markets upon which the Company has focused.  The Company is not
aware of the development of any experimental agents which are targeted
specifically for these markets, although many companies do not publish or
otherwise distribute information about their products under development.



                                     15

<PAGE>   16

The technology of the Company's subsidiary, ATI, also is highly competitive.
ATI is expected to face competition from other biotechnological approaches as
well as more traditional, drug-based approaches to cancer and viral diseases.
ATI will experience competition from fully integrated pharmaceutical companies
with expertise in research and development, manufacturing and product
commercialization, and which have greater resources in these areas than ATI.
The Company also is aware of numerous development-stage companies that are
exploring new therapies for the same disease targets as ATI.

REGULATORY ISSUES

ImmunoGen's products are regulated in the United States by FDA in accordance
with the Federal Food, Drug, and Cosmetic Act as well as the Public Health
Service Act.  Parenteral monoclonal antibody products are most often considered
biologicals and therefore subject to regulation by the Center for Biologics
Evaluation and Research within FDA.  Thus, human clinical trials of a new
product are conducted after submission of an IND application acceptable to FDA
and commercial marketing of that product may occur only after approval of a PLA
and an Establishment License Application ("ELA").  Manufacturing must be
performed in accordance with Good Manufacturing Practices ("GMPs").

The regulatory issues that have potential impact on future marketing of
ImmunoGen products are summarized in the following paragraphs:

CLINICAL TRIALS PROCESS.  Before a pharmaceutical product may be sold in the
United States and other countries, clinical trials of the product must be
conducted and the results submitted to the appropriate regulatory agencies for
approval.

In the United States, these clinical trial programs generally involve a
three-phase process.  Typically, Phase I trials are conducted in healthy
volunteers to determine the early side-effect profile and the pattern of drug
distribution and metabolism.  In Phase II, trials are conducted in groups of
patients afflicted with the target disease to determine preliminary efficacy
and optimal dosages and to expand the safety profile.  In Phase III,
large-scale comparative trials are conducted in patients with the target
disease to provide sufficient data for the proof of efficacy and safety
required by federal regulatory agencies.  In the case of drugs for cancer and
other life-threatening diseases, Phase I human testing is performed in patients
with advanced disease rather than in healthy volunteers.  Because these
patients are already afflicted with the target disease, it is possible for such
studies to provide results traditionally obtained in Phase II trials and they
often are referred to as Phase I/II studies.

The Company also will be subject to widely varying foreign regulations
governing clinical trials and pharmaceutical sales.  Whether or not FDA
approval has been obtained, approval of a product by the comparable regulatory
authorities of foreign countries must be obtained prior to the commencement of
marketing of the product in those countries.  The approval process varies from
country to country and the time may be longer or shorter than that required for
FDA approval.  The Company intends to rely on foreign licensees to obtain
regulatory approvals to market ImmunoGen products in foreign countries.

Regulatory approval often takes a number of years and involves the expenditure
of substantial resources.  Approval times also depend on a number of factors,
including the severity of the disease in question, the availability of
alternative treatments and the risks and benefits demonstrated in clinical
trials.

ORPHAN DRUG DESIGNATION.  The Orphan Drug Act of 1983 generally provides
incentives to manufacturers to undertake development and marketing of products
to treat relatively rare diseases or diseases affecting fewer than 200,000
persons in the United States at the time of application for Orphan 



                                     16

<PAGE>   17

Drug designation.  Orphan Drug designation has been granted for Oncolysin B,
Oncolysin S, Oncolysin M and Oncolysin CD6.

ImmunoGen will continue to pursue this designation with respect to all of its
products intended for qualifying patient populations.  A drug that receives
Orphan Drug designation and is the first product to receive FDA marketing
approval for its product claim is entitled to a seven-year exclusive marketing
period in the United States for that product claim.  However, a drug that is
considered by the FDA to be different from a particular Orphan Drug is not
barred from sale in the United States during such seven-year exclusive
marketing period.

TREATMENT IND STATUS.  ImmunoGen may file for Treatment IND status for some
indications under provisions of the IND regulations revised in 1987.  These
regulations apply to products for patients with serious or life-threatening
diseases and are intended to facilitate the availability of new products to
desperately ill patients after clinical trials have shown convincing evidence
of efficacy, but before general marketing approval has been granted by FDA.
Under these regulations, the Company anticipates that it will be in a position
to recover some of the costs of research, development and manufacture of its
products before marketing begins.

DRUGS FOR LIFE-THREATENING ILLNESSES.  FDA regulations issued in October 1988
are intended to speed the availability of new therapies to desperately ill
patients.  These procedures permit early consultation and commitment from FDA
regarding preclinical and clinical studies necessary to gain marketing
approval.  Additional FDA regulations issued in December 1992 define
opportunities for accelerated review and approval of therapies for serious or
life-threatening illnesses.  Guidelines for FDA accelerated review, articulated
in November 1991 by the President's Council on Competitiveness, state that by
1994 such reviews should be made within six months.  The Company believes that
certain applications for its products qualify for accelerated review.

RESEARCH AND DEVELOPMENT SPENDING

During each of the three years ended June 30, 1993, 1994 and 1995 the Company
spent approximately $17.1 million, $19.9 million and $16.8 million,
respectively, on research and development activities. Most of these
expenditures were for Company-sponsored research and development.

EMPLOYEES

As of June 30, 1995, the Company had 76 full-time employees,  of whom 21 hold
Ph.D. or M.D. degrees. The Company considers its relations with its employees
to be good and has experienced a low rate of employee attrition relative to
other companies in the industry. None of the Company's employees is covered by
a collective bargaining agreement. The Company has entered into confidentiality
agreements with all of its employees, members of the Scientific Advisory Board
and other consultants.

SCIENTIFIC ADVISORY BOARDS
  IMMUNOGEN, INC.

At June 30, 1995 the members of the Company's Scientific Advisory Board were as
follows:

Baruj Benacerraf, M.D.  Chairman of the Scientific Advisory Board; President,
Dana-Farber, Inc. and Fabyan Professor of Comparative Pathology, Emeritus,
Harvard University Medical School; 1980 Nobel Prize in Physiology or Medicine.


                                     17

<PAGE>   18

Emil Frei, III, M.D.  Physician-in-Chief, Emeritus, and Chief, Division of
Cancer Pharmacology, Dana-Farber Cancer Institute and Richard and Susan Smith
Professor of Medicine, Harvard University Medical School; 1983 Kettering Prize.

Stuart F. Schlossman, M.D.  Professor of Medicine, Harvard University Medical
School;  member of the National Academy of Sciences; Head of the Division of
Tumor Immunology of Dana-Farber Cancer Institute.

  APOPTOSIS TECHNOLOGY, INC.

Paul J. Anderson, M.D., Ph.D. Assistant Professor of Medicine, Harvard
University Medical School; Associate Rheumatologist,  Brigham & Women's
Hospital; associated with Dana-Farber Cancer Institute since 1986. Dr. Anderson
has received numerous awards for excellence in research, and is a member of the
American Association of Immunologists and a Fellow of the American College of
Rheumatology.

Walter A. Blattler, Ph.D. Vice President of Research, ATI and Chairman of the
ATI Scientific Advisory Board. Dr. Blattler received his Ph.D. from the Swiss
Federal Institute of Technology (ETH) in Zurich in 1978. He was the founding
scientist of ImmunoGen, Inc. and currently serves as ImmunoGen's Vice President
for Research.

Gerard Evan, Ph.D. Principal Scientist and Head of Biochemistry of the Cell
Nucleus Laboratory, Imperial Cancer Research Fund. Dr. Evan received his Ph.D.
from the University of Cambridge and MRC Laboratory of Molecular Biology and is
an authority on the control of cellular proliferation and programmed cell death
in mammalian cells.

Elliott D. Kieff, M.D., Ph.D., Professor of Medicine and Professor of
Microbiology and Molecular Genetics, Harvard University Medical School;
Director of Infectious Diseases,  Brigham and Women's Hospital; Chairman of
Virology at Harvard University and an authority on herpes viruses.

Stuart F. Schlossman, M.D. Professor of Medicine, Harvard University Medical
School;  member of the National Academy of Sciences; Head of the Division of
Tumor Immunology of Dana-Farber Cancer Institute.


I
TEM 2.  PROPERTIES

ImmunoGen leases approximately 52,700 square feet of laboratory and office
space at two locations in Cambridge, Massachusetts, of which approximately
30,800 square feet has been subleased by the Company as of September 1, 1995.
The Company also leases 27,500 square feet of space in Norwood, Massachusetts,
which is currently the Company's pilot manufacturing facility, and 47,000
square feet of space in Canton, Massachusetts, which have been idle since the
Company implemented its restructuring plan in December 1994. The Company
believes that the manufacturing portion of each of the Norwood and Canton
facilities, although not yet inspected by the FDA, complies with all applicable
FDA Good Manufacturing Practice Regulations.


ITEM 3. LEGAL PROCEEDINGS

Not applicable.


                                     18

<PAGE>   19


ITEM 4. SUBMISSION OF MATTERS TO A VOTE OF SECURITY HOLDERS

Not applicable.

DIRECTORS AND EXECUTIVE OFFICERS

See Item 10 below.


PART II


<TABLE>

ITEM 5. MARKET PRICE OF AND DIVIDENDS ON THE REGISTRANT'S COMMON EQUITY AND
RELATED STOCKHOLDER MATTERS

ImmunoGen's Common Stock is traded in the over-the-counter market and is quoted
in the Nasdaq National Market System under the symbol IMGN. The table below
sets forth the high and low sale prices for ImmunoGen Common Stock for each of
the quarters indicated during the Company's last two fiscal years.

<CAPTION>
Fiscal Year 1995                   HIGH                LOW
     <S>                           <C>                 <C>
     First Quarter                  5 1/8              2 5/8
     Second Quarter                 5                  1 7/8
     Third Quarter                  2 23/32            1 3/4
     Fourth Quarter                 4                  1 3/4

<CAPTION>
Fiscal Year 1994                   HIGH                LOW
     First Quarter                  8                  5 1/4
     Second Quarter                11                  7 1/4
     Third Quarter                  9 3/4              5 1/2
     Fourth Quarter                 6                  3 1/2

</TABLE>


As of June 30, 1995, there were approximately 729 holders of record of the
Company's Common Stock and, according to the Company's estimates, approximately
9,500 beneficial owners of the Company's Common Stock.

The Company has not paid any cash dividends on its Common Stock since its
inception and does not intend to pay any cash dividends in the foreseeable
future.


                                     19

<PAGE>   20
     

<TABLE>

ITEM 6. SELECTED FINANCIAL DATA

The following table sets forth consolidated financial data with respect to the
Company for each of the five years in the period ended June 30, 1995. The
information set forth below should be read in conjunction with "Management's
Discussion and Analysis of Financial Condition and Results of Operations" and
the consolidated financial statements and related notes included elsewhere in
this 10-K report.
<CAPTION>
                                                         Year Ended June 30,
                               ---------------------------------------------------------------------------
                                    1991            1992            1993            1994            1995
                               ---------------------------------------------------------------------------
                                                (in thousands, except per share data)
<S>                            <C>             <C>             <C>             <C>             <C>
Total revenues                 $    3,368      $    2,770      $     1,658     $       926     $       512
Total expenses                     12,112          18,074           20,274          24,606          20,363
Net loss                           (8,814)        (15,344)         (18,634)        (23,690)        (19,857)
Loss per share
  of common stock                   (1.28)          (1.58)           (1.76)          (2.09)          (1.58)
Total assets                       44,422          62,036           46,458          38,384          17,046
Capital lease obligations,
  less current portion                648             551            1,212           3,338           2,331
Stockholders' equity               41,988          59,080           40,540          29,960          10,123

Weighted average
 shares outstanding             6,882,852       9,702,988       10,617,109      11,332,194      12,571,134
</TABLE>



                                      20

<PAGE>   21



ITEM 7.  MANAGEMENT'S DISCUSSION AND ANALYSIS OF
FINANCIAL CONDITION AND RESULTS OF OPERATIONS

OVERVIEW

Since its inception, ImmunoGen has been primarily engaged in research and
development of immunoconjugate products which it believes have significant
commercial potential as human therapeutics.  The major sources of the Company's
working capital have been the proceeds of equity financings, license fees and
income earned on the investment of those funds.

In an action to reduce costs, the Company in December 1994 implemented a
restructuring plan, suspending its operations at its Canton and Norwood,
Massachusetts production facilities, reducing or eliminating certain areas of
research and focusing its clinical efforts on its first product.  This plan
resulted in the termination of approximately 100 employees and affected all
functional areas within the Company.  Restructuring charges approximating
$643,000 were charged to expense in December 1994 representing severance costs
for terminated employees.  As of June 30, 1995 all costs related to the plan
had been paid.

In a further cost reduction effort, the Company entered into an agreement
effective September 1, 1995 to sublease approximately 82% of one of its
Cambridge, Massachusetts facilities.  The initial term of this agreement
expires in February 1997 (with two one-year renewal options).

The Company has been unprofitable since inception and incurred net operating
losses of $18.6 million in fiscal 1993, $23.7 million in fiscal 1994 and $19.9
million in fiscal 1995.  The Company expects to incur net losses over the next
several years.

RESULTS OF OPERATIONS

Revenues in fiscal 1993, 1994 and 1995 were derived principally from interest
income on the proceeds of the Company's equity offerings. Smaller amounts of
development revenues were received under the Small Business Innovative Research
Program of the U.S. National Science Foundation and under the Orphan Product
Development Program of the U.S. Department of Health and Human Services.  In
addition, a gain on sale of assets which resulted from a sale/leaseback
agreement executed in March 1994 has been deferred and is being recorded as
other income over the life of the lease.

Interest income decreased 44% from approximately $1.5 million in fiscal 1993 to
approximately $0.8 million in fiscal 1994 and then decreased 45% to
approximately $0.5 million in fiscal 1995.  These decreases are attributable to
the lower cash balances available for investment between these periods.

The Company's total expenses increased 21% from approximately $20.3 million in
fiscal 1993 to approximately $24.6 million in fiscal 1994 and then decreased
17% to approximately $20.4 million in fiscal 1995.  Research and development
costs constituted the primary component of the Company's total expenses (84%,
81% and 83% in fiscal 1993, 1994 and 1995, respectively) increasing from
approximately $17.1 million in fiscal 1993 to approximately $19.9 million in
fiscal 1994 and then decreasing to approximately $16.8 million in fiscal 1995.
The 17% increase between fiscal 1993 and fiscal 1994 resulted largely from
continued expansion of the Company's medical affairs department to support
ongoing clinical trials, full-year operations of the Company's 72%-owned
subsidiary, Apoptosis Technology, Inc. ("ATI"), commencement of operations at
the Company's Canton, Massachusetts facility and certain facilities costs of
the Company's new Cambridge, Massachusetts facility allocated to research 



                                      21

<PAGE>   22
and development.  The 16% decrease between fiscal 1994 and fiscal 1995 is the
result of the Company's restructuring plan implemented in December 1994, offset
somewhat by increased costs associated with ATI and increased non-cash
depreciation charges associated with the capital expenditures made in prior
periods.  A planned substantial reduction in raw materials purchases in fiscal
1995 also contributed to the decrease in expenses.

General and administrative expenses increased 43% from approximately $3.1
million in fiscal 1993 to approximately $4.5 million in fiscal 1994 and then
decreased 33% to approximately $3.0 million in fiscal 1995.  Increases from
fiscal 1993 to fiscal 1994 were due largely to the facilities costs associated
with the new Cambridge facility allocated to administration, increases in the
Company's management information services and business development efforts,
increased director and officer liability insurance costs and severance costs to
one of the Company's former senior executives.  Decreases from fiscal 1994 to
fiscal 1995 represented savings associated with the restructuring plan and
reductions in management and administrative staff in the second and third
quarters of calendar 1994, offset somewhat by the restructuring charges
incurred.

Interest expense increased 167% from approximately $65,000 in fiscal 1993 to
approximately $174,000 in fiscal 1994 and increased 193% to approximately
$510,000 in fiscal 1995 as the Company utilized capital lease arrangements to
finance certain equipment and leasehold improvements at its Canton production
facility.

LIQUIDITY AND CAPITAL RESOURCES

Since July 1, 1992 the Company has financed its operating deficit of $62.2
million from various sources, including net proceeds of $13.0 million raised in
its fiscal 1994 public offering and from the exercise of stock options.  Since
July 1, 1992 the Company has received approximately $0.2 million from
development and licensing revenues and $2.8 million of interest income.  At
June 30, 1995 approximately $3.0 million of cash and cash equivalents remained
available.

In February 1994 the Company sold in a public offering 2,012,500 shares of its
common stock.  Net proceeds to the Company amounted to $13,242,250.  In March
1994 the Company executed a sale/leaseback agreement to finance approximately
$4.0 million of equipment at the Canton facility.  At June 30, 1994 all monies
available under this agreement had been received.  The transaction included
warrants to purchase common stock which expire in April 1999.

In August 1995 the Company issued $3.6 million of subordinated convertible
debentures, due July 31, 1996, in a private placement to a small number of
foreign investors.  Net proceeds to the Company amounted to approximately $3.3
million.  Subject to certain restrictions, the debentures are convertible to
common stock, at the holders' discretion, at any time between October 1995 and
July 1996.

In the period since July 1, 1992 approximately $16.3 million was expended on
property and equipment, including the equipment sold and leased back,
principally for construction of the Company's manufacturing facilities in
Norwood, Massachusetts.  No significant amounts are expected to be expended on
property and equipment in fiscal 1996.

Pursuant to its agreements with ATI, the Company committed to provide ATI with
$3.0 million in research and development services and $2.0 million of cash
equity contributions.  At June 30, 1995 these obligations had been fulfilled by
the Company.  ImmunoGen has also agreed to obtain or furnish an additional $3.0
million in equity for ATI on such terms and conditions as may be mutually
agreed to by 



                                      22

<PAGE>   23

ATI and the providers of such additional equity.  The Company anticipates that
approximately $650,000 of funding may be required by ATI during calendar year
1996 in order for ATI to satisfy certain contractual obligations.

The Company anticipates that its existing capital resources will enable it to
maintain its current and planned operations through January 1996.  Because of
its continuing losses from operations and working capital deficit, the Company
will be required to obtain additional capital to satisfy its ongoing capital
needs and to continue its operations.  Although managment continues to pursue
additional funding arrangements, no assurance can be given that such financing
will in fact be available to the Company.  If the Company is unable to obtain
financing on acceptable terms in order to maintain operations through the next
fiscal year, it could be forced to curtail or discontinue its operations.




                                      23

<PAGE>   24

<TABLE>

I
TEM 8. FINANCIAL STATEMENTS
Index to Consolidated Financial Statements

<CAPTION>
                                                                        Page
- ----------------------------------------------------------------------------
<S>                                                                       <C>
Report of Independent Accountants                                         25
Consolidated Financial Statements:
     Consolidated Balance Sheets at June 30, 1994 and 1995                26
     Consolidated Statements of Operations for the Years
          Ended June 30, 1993, 1994 and 1995                              27
     Consolidated Statements of Stockholders' Equity
          for the Years Ended June 30, 1993, 1994 and 1995                28
     Consolidated Statements of Cash Flows for the Years
          Ended June 30, 1993, 1994 and 1995                              29
     Notes to Consolidated Financial Statements                           30



</TABLE>










                                      24

<PAGE>   25




REPORT OF INDEPENDENT ACCOUNTANTS

TO THE BOARD OF DIRECTORS AND SHAREHOLDERS OF IMMUNOGEN, INC.:

We have audited the accompanying consolidated balance sheets of ImmunoGen, Inc.
as of June 30, 1994 and 1995, and the related consolidated statements of
operations, stockholders' equity and cash flows for each of the three years in
the period ended June 30, 1995. These financial statements are the
responsibility of the Company's management. Our responsibility is to express an
opinion on these financial statements based on our audits.

We conducted our audits in accordance with generally accepted auditing
standards. These standards require that we plan and perform the audit to obtain
reasonable assurance about whether the financial statements are free of
material misstatement. An audit includes examining, on a test basis, evidence
supporting the amounts and disclosures in the financial statements. An audit
also includes assessing the accounting principles used and significant
estimates made by management, as well as evaluating the overall financial
statement presentation. We believe that our audits provide a reasonable basis
for our opinion.

In our opinion, the financial statements referred to above present fairly, in
all material respects, the consolidated financial position of ImmunoGen, Inc.
as of June 30, 1994 and 1995 and the consolidated results of its operations and
its cash flows for each of the three years in the period ended June 30, 1995,
in conformity with generally accepted accounting principles.

The accompanying financial statements have been prepared assuming that the
Company will continue as a going concern.  As discussed in Note A, the Company
has suffered recurring losses from operations, has a net working capital
deficit and requires significant  additional financing.  These factors raise
substantial doubt about the Company's ability to continue as a going concern.
Management's plans in regard to these matters are also described in Note A.
The financial statements do not include any adjustments that might result from
the outcome of this uncertainty.


                              /s/Coopers & Lybrand L.L.P.
                              ---------------------------

                              COOPERS & LYBRAND L.L.P.



Boston, Massachusetts
September 1, 1995

<PAGE>   26

<TABLE>
IMMUNOGEN, INC.

CONSOLIDATED BALANCE SHEETS

As of June 30, 1994 and 1995
<CAPTION>

                                                                       June 30,
                                                          ------------------------------------                        
                                                           
                                                                  1994                    1995
- ----------------------------------------------------------------------------------------------
<S>                                                       <C>                    <C>
ASSETS                                                                           
                                                                                  
Cash and cash equivalents                                 $  1,572,389           $   3,047,236
Marketable securities                                       19,629,177                       -
Other current assets                                           629,809                 293,852
                                                          ------------------------------------                        
                                                                                  
      Total current assets                                  21,831,375               3,341,088
                                                          ------------------------------------                        
                                                                                  
Property and equipment, net of accumulated                                        
   depreciation (Notes E and H)                             16,468,761              13,621,383
Other assets                                                    83,700                  83,700
                                                          ------------------------------------                        
           Total assets                                   $ 38,383,836           $  17,046,171
                                                          ====================================                        
                                                                                  
LIABILITIES AND STOCKHOLDERS' EQUITY                                              
                                                                                  
Accounts payable (Note D)                                    2,209,151               2,229,003
Accrued compensation (Note K)                                  936,914                 316,973
Other accrued liabilities (Note D)                             929,978                 978,253
Current portion of capital lease obligations (Note H)          828,954                 942,749
                                                          ------------------------------------                        
                                                                                  
      Total current liabilities                              4,904,997               4,466,978
                                                          ------------------------------------                        
                                                                                  
Capital lease obligations (Note H)                           3,337,932               2,330,680
Other non-current liabilities  (Note H)                        181,067                 125,354
                                                                                  
Commitments (Notes D and H)                                                       
                                                                                  
Redeemable convertible preferred stock,                                           
   $.01 par value; authorized 277,080 shares;                                     
   none issued (Note G)                                              -                       -
                                                                                  
Stockholders' equity (Note G):                                                    
   Common stock, $.01 par value; authorized                                       
      20,000,000 shares; issued and outstanding                                   
      12,554,731 and, 12,578,606 shares as of                                     
      June 30, 1994 and 1995, respectively                     125,547                 125,786
   Additional paid-in capital                              118,968,588             118,988,736
                                                          ------------------------------------                        
                                                                                  
                                                           119,094,135             119,114,522
   Accumulated deficit                                     (89,134,295)           (108,991,363)
                                                          ------------------------------------                        
                                                                                  
      Total stockholders' equity                            29,959,840              10,123,159
                                                          ------------------------------------                        

           Total liabilities and stockholders' equity     $ 38,383,836           $  17,046,171
                                                          ====================================                        

</TABLE>







   The accompanying notes are an integral part of the financial statements.

                                      26

<PAGE>   27

<TABLE>
IMMUNOGEN, INC.

CONSOLIDATED STATEMENTS OF OPERATIONS

For the years ended June 30, 1993, 1994 and 1995
<CAPTION>
                                                                    June 30,
                                         -------------------------------------------------------
                                          
                                                 1993                1994                   1995
- ------------------------------------------------------------------------------------------------
<S>                                      <C>                 <C>                    <C>
Revenues:                                                     
   Development fees (Note D)             $    158,810        $     74,700
   Interest                                 1,486,852             839,005           $    459,293
   Other (Note D)                              12,554              12,504                 52,571
                                         -------------------------------------------------------
                                                                                     
      Total revenues                        1,658,216             926,209                511,864
                                         -------------------------------------------------------
                                                                                     
Expenses:                                                                            
   Research and development (Note D)       17,067,162          19,929,474             16,819,082
   General and administrative               3,141,512           4,502,259              3,034,087
   Interest (Note H)                           65,188             173,867                509,700
                                         -------------------------------------------------------
                                                                                     
      Total expenses                       20,273,862          24,605,600             20,362,869
                                         -------------------------------------------------------
                                                                                     
                                                                                     
Loss before income taxes                  (18,615,646)        (23,679,391)           (19,851,005)
                                                                                     
Income tax expense (Note F)                    18,214              11,075                  6,063
                                         -------------------------------------------------------
                                                                                     
Net loss                                 $(18,633,860)       $(23,690,466)          $(19,857,068)
                                         =======================================================
                                                                                     
Loss per common share (Note C)           $      (1.76)       $      (2.09)          $      (1.58)
                                         =======================================================
                                                                                     
Shares used in computing loss                                                        
   per share amounts (Note C)              10,617,109          11,332,194             12,571,134
                                         =======================================================
</TABLE>




   The accompanying notes are an integral part of the financial statements.


                                      27

<PAGE>   28

<TABLE>
IMMUNOGEN, INC.

CONSOLIDATED STATEMENTS OF 
STOCKHOLDERS' EQUITY

For the years ended June 30, 1993, 
1994 and 1995
<CAPTION>
                                                                  Common Stock
                                                      -------------------------------------
                                                                                Additional                       Total
                                                                                 Paid-in       Accumulated    Stockholders'
                                                        Shares        Amount     Capital         Deficit         Equity
                                                      --------------------------------------------------------------------
<S>                                                   <C>           <C>        <C>            <C>             <C>
Balance at June 30, 1992                              10,394,695    $103,947   $105,786,115   $ (46,809,969)  $ 59,080,093
                                                      --------------------------------------------------------------------

Issuance of common stock                                 104,098       1,041         92,871               -         93,912
Net loss for the year ended June 30, 1993                      -           -              -     (18,633,860)   (18,633,860)
                                                      --------------------------------------------------------------------
                                                                                                               
Balance at June 30, 1993                              10,498,793     104,988    105,878,986     (65,443,829)    40,540,145
                                                      --------------------------------------------------------------------
                                                                                                               
Issuance of common stock                               2,055,938      20,559     13,012,864               -     13,033,423
Issuance of common stock warrants                                                    76,738                         76,738
Net loss for the year ended June 30, 1994                      -              -           -     (23,690,466)   (23,690,466)
                                                      --------------------------------------------------------------------
                                                                                                               
Balance at June 30, 1994                              12,554,731     125,547    118,968,588     (89,134,295)    29,959,840
                                                      --------------------------------------------------------------------
                                                                                                               
Stock options excercised                                  23,875         239         20,148               -         20,387
Net loss for the year ended June 30, 1995                      -           -              -     (19,857,068)   (19,857,068)
                                                      --------------------------------------------------------------------
                                                                                                               
Balance at June 30, 1995                              12,578,606    $125,786   $118,988,736   $(108,991,363)  $ 10,123,159
                                                      ====================================================================
</TABLE>


   The accompanying notes are an integral part of the financial statements.


                                      28


<PAGE>   29

<TABLE>
IMMUNOGEN, INC.

CONSOLIDATED STATEMENTS OF CASH FLOWS

For the years ended June 30, 1993, 1994 and 1995
<CAPTION>
                                                                                          June 30,
                                                                  ---------------------------------------------------- 
                                                                            1993               1994              1995
                                                                  ----------------------------------------------------
<S>                                                               <C>                  <C>                <C>
Cash flows from operating activities:                                                                      
   Net loss                                                       $  (18,633,860)      $(23,690,466)      $(19,857,068)
   Adjustments to reconcile net loss to net                                                                
      cash used for operating activities:                                                                  
        Depreciation and amortization                                  1,664,750          2,031,477          3,350,685
        (Gain)/Loss on sale of property and equipment                          -              4,888            (15,630)
        Changes in operating assets and liabilities:                                                       
          Other current assets                                          (211,887)            18,988            335,957
          Other assets                                                  (410,471)           392,015                  -
          Accounts payable                                             1,030,736           (566,100)            19,852
          Accrued compensation                                           165,913            531,073           (619,941)
          Accrued construction costs                                     616,816           (616,816)                 -
          Other accrued liabilities                                      374,204            176,728             48,275
          Other non-current liabilities                                        -            250,709                  -
                                                                  ----------------------------------------------------
                                                                                                           
        Net cash used for operating activities                       (15,403,799)       (21,467,504)       (16,737,870)
                                                                  ----------------------------------------------------
                                                                                                           
Cash flows from investing activities:                                                                      
   Capital expenditures                                               (8,216,379)        (7,628,278)          (477,288)
   Proceeds from sale of marketable securities                        56,960,818         40,967,462         30,505,763
   Purchase of marketable securities                                 (62,660,419)       (35,685,475)       (10,925,635)
                                                                  ----------------------------------------------------
                                                                                                           
        Net cash provided by (used for)                                                                    
         investing activities                                        (13,915,980)        (2,346,291)        19,102,840
                                                                  ----------------------------------------------------
                                                                                                           
Cash flows from financing activities:                                                                      
   Stock issuances, net                                                   93,912         13,033,423             20,387
   Proceeds from sale/leaseback transactions                             871,417          4,015,330                  -
   Principal payments on capital lease obligations                       (97,033)        (1,197,999)          (910,510)
                                                                  ----------------------------------------------------
                                                                                                           
        Net cash provided by (used for)                                                                    
         financing activities                                            868,296         15,850,754           (890,123)
                                                                  ----------------------------------------------------
                                                                                                           
Net change in cash and cash equivalents                              (28,451,483)        (7,963,041)         1,474,847
                                                                  ----------------------------------------------------
                                                                                                           
Cash and cash equivalents, beginning balance                          37,986,913          9,535,430          1,572,389
                                                                  ----------------------------------------------------
                                                                                                           
Cash and cash equivalents, ending balance                         $    9,535,430       $  1,572,389       $  3,047,236
                                                                  ====================================================
                                                                                                           
Supplemental disclosure of cash flow information:                                                          
                                                                                                           
   Cash paid for interest                                         $       65,188       $    156,669       $    513,635
                                                                  ====================================================
   Cash paid (refunded) for income taxes                          $       18,216       $     12,310       $     (4,390)
                                                                  ====================================================
</TABLE>



   The accompanying notes are an integral part of the financial statements.


                                      29


<PAGE>   30

IMMUNOGEN, INC.

NOTES TO CONSOLIDATED FINANCIAL STATEMENTS

A.  NATURE OF BUSINESS AND PLAN OF OPERATION:

ImmunoGen, Inc. (the "Company") was incorporated in Massachusetts on March 27,
1981.  The Company was formed to develop, produce and market commercial cancer
and other pharmaceuticals based on molecular immunology.  The Company continues
research and development of its various products, and expects no revenues to be
derived from product sales in the near future.

In an action to reduce costs, the Company in December 1994 implemented a
restructuring plan, suspending its operations at its Canton and Norwood,
Massachusetts production facilities (with a net book value of approximately
$8.8 million), reducing or eliminating certain areas of research and focusing
its clinical efforts on certain products.  This plan resulted in the
termination of approximately 100 employees and affected all functional areas
within the Company.  Restructuring charges approximating $643,000 were charged
to expense in December 1994 representing severance costs for terminated
employees.  As of June 30, 1995 all severance costs have been paid.

In a further reduction effort, the Company entered into an agreement effective
September 1, 1995 to sublease approximately 82% of one of its Cambridge,
Massachusetts facilities. This initial lease term expires in February 1997,
with two one-year renewal options.

In August 1995 the Company issued $3.6 million of 7% subordinated convertible
debentures, due July 31, 1996, in a private placement to a small number of
overseas investors.  Subject to certain restrictions, the debentures are
convertible to common stock, at the holders' discretion at any time between
October 1995 and July 1996.

Because of its continuing losses from operations and working capital deficit,
the Company will be required to obtain additional capital in the short term to
satisfy its ongoing capital needs and to continue its operations.  Although
management continues to pursue additional funding arrangements and/or strategic
partnering, no assurance can be given that such financing will in fact be
available to the Company.  If the Company is unable to obtain financing on
acceptable terms in order to maintain operations through the next fiscal year,
it could be forced to curtail or discontinue its operations.  The financial
statements do not include any adjustments that might result from the outcome of
this uncertainty.

B.  SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES:

  PRINCIPLES OF CONSOLIDATION

The consolidated financial statements include the accounts of the Company and
its wholly-owned subsidiary, ImmunoGen Securities Corp. (established in
December 1989), and its 72%-owned subsidiary, Apoptosis Technology, Inc.
("ATI") (established in January 1993) (see Note D).  All intercompany activity
has been eliminated.

  RESEARCH AND DEVELOPMENT COSTS

Research and development costs are expensed as incurred.


                                      30

<PAGE>   31

IMMUNOGEN, INC.
NOTES TO CONSOLIDATED FINANCIAL STATEMENTS, CONTINUED

 CASH, CASH EQUIVALENTS AND MARKETABLE SECURITIES

The Company considers all investments purchased with maturity dates of three
months or less from date of acquisition to be cash equivalents.

Cash and cash equivalents include, at cost plus accrued interest which
approximates market value, $1,572,389 and $3,047,236 of money market funds,
demand notes and repurchase agreements at June 30, 1994 and 1995, respectively.

As of June 30, 1994, marketable securities, consisting primarily of U.S.
Government debt securities of approximately $19.6 million, were carried at
amortized cost which approximates market value.

In fiscal 1995 the Company implemented Financial Accounting Standard (SFAS) No.
115, "Accounting for Certain Investments in Debt and Equity Securities."  The
impact was immaterial to its financial position and results of operations.

   CONCENTRATION OF CREDIT RISK

The Company minimizes the risk associated with concentration of credit by
utilizing the services of more than one custodian for its cash and assuring
that financial instruments purchased by its cash managers include only
high-grade, low-risk investments.  At June 30, 1994 and 1995, those investments
included various U.S. Government securities, money market investments with
major financial institutions and cash on deposit with major banks.


<TABLE>
   PROPERTY AND EQUIPMENT
                                       
Property and equipment are stated at cost.  The Company provides for
depreciation based upon expected useful lives using the straight-line method
over the following estimated useful lives:

          <S>                                      <C>
          Machinery and equipment................. 3-5 years
          Computer hardware and software.......... 5 years
          Furniture and fixtures.................. 5 years
          Leasehold improvements.................. Shorter of lease term or
                                                   estimated useful life
</TABLE>


Maintenance and repairs are charged to expense as incurred.  Upon retirement or
sale, the cost of disposed assets and the related accumulated depreciation are
removed from the accounts and any resulting gain or loss is credited or charged
to operations.  Gains recorded under sale/leaseback arrangements are deferred
and amortized to operations over the life of the lease.

  INCOME TAXES

The Company uses the liability method whereby the deferred tax liabilities and
assets are recognized based on temporary differences between the financial
statement and tax basis of assets and liabilities using current statutory tax
rates.  A valuation allowance against net deferred tax assets is recorded if,


                                      31

<PAGE>   32

IMMUNOGEN, INC.
NOTES TO CONSOLIDATED FINANCIAL STATEMENTS, CONTINUED

based on the weighted available evidence, it is more likely than not that some
or all of the deferred tax assets will not be realized.

C.  LOSS PER COMMON SHARE:

Net loss per common share is based on the weighted average number of common
shares outstanding during the periods.  Common share equivalents have not been
included because their effect would be anti-dilutive.  Fully diluted earnings
per share are the same as primary earnings per share.

D.  AGREEMENTS:

The Company has a long-standing research and license agreement with the
Dana-Farber Cancer Institute, Inc. ("Dana-Farber"), a Massachusetts
not-for-profit corporation.  As part of the agreement, the Company has agreed
to fund certain research and development projects conducted by Dana-Farber in
relation to the development and eventual commercialization of certain
biologicals to be used in the treatment of certain forms of cancer.  In fiscal
years 1993, 1994 and 1995 the Company incurred research and development
expenses of approximately $825,000, $567,000 and $225,000 respectively, in
connection with this agreement.  To the extent that an invention is developed
at Dana-Farber with principal support and funding by the Company, the Company
shall have the exclusive right to use the invention.  As part of this
arrangement, the Company is required to pay to Dana-Farber, when product sales
commence, certain royalties based on a formula stipulated in the agreement.
The Company owed Dana-Farber approximately $1,207,000 and $1,169,000 at June
30, 1994 and 1995, respectively, for work performed under this agreement.

The agreement also contains provisions, which expired in June 1994, whereby
Dana-Farber is required to pay to the Company a percentage of royalties
received by Dana-Farber in consideration for the Company's consulting in
connection with the identification of a commercial entity through which
Dana-Farber can develop and market certain antibodies of its own. The Company
earned royalties under these provisions of approximately $13,000 in each of
fiscal years 1993 and 1994.

In January 1993, the Company purchased 7,000 shares of Class A Preferred Stock
of ATI.  ATI is a joint venture between ImmunoGen and Dana-Farber established
to develop therapeutics based on apoptosis technology developed at Dana-Farber.
ATI is the licensee of Dana-Farber's apoptosis technology.  Under an agreement
entered into between ATI and ImmunoGen, subject to certain provisions of the
agreement between ATI and Dana-Farber, ImmunoGen has the exclusive right to
license products developed by ATI, including those based on Dana-Farber's
apoptosis technology.

The Preferred Stock is voting stock and carries a liquidation preference over
the common stock.  The Company's investment represents 72% of the currently
authorized equity of ATI and, accordingly, is consolidated.  In addition, the
Company has a right of first refusal to purchase any ATI shares which may be
offered for sale by the other current stockholders of ATI.  If ATI has not
concluded a public offering of its stock for at least $5.0 million prior to
January 11, 1998, the other stockholders (currently representing 2,765 shares
of common stock) of ATI can require ImmunoGen to purchase, or ImmunoGen can
require such stockholders to sell, their shares in ATI at a predetermined
price.  At ImmunoGen's option, the shares of common stock of ATI can be paid
for in cash or by delivery of shares of ImmunoGen common stock.


                                      32

<PAGE>   33
IMMUNOGEN, INC.
NOTES TO CONSOLIDATED FINANCIAL STATEMENTS, CONTINUED

A portion of the Company's research and development expenses was incurred in
connection with an agreement between ATI and Dana-Farber, under which ATI has
agreed to fund certain research projects conducted at Dana-Farber.  In fiscal
1993, 1994 and 1995 these expenses amounted to approximately $273,000, $530,000
and $670,000, respectively.

ImmunoGen was committed to provide ATI with $3.0 million in research and
development services and $2.0 million in cash equity contributions over a
three-year period.  At June 30, 1995 these obligations had been fulfilled by
the Company.  ImmunoGen has also agreed to obtain or furnish an additional $3.0
million in equity for ATI on such terms and conditions as may be mutually
agreed to by ATI and the providers of such additional equity.

Development revenues of approximately $159,000 and $75,000 in fiscal 1993 and
1994, respectively, represent payments received under the Small Business
Innovative Research Program of the U.S. National Science Foundation and under
the Orphan Product Development Program of the U.S. Department of Health and
Human Services.



<TABLE>
E.  PROPERTY AND EQUIPMENT:

Property and equipment consisted of the following at June 30, 1994 and 1995:

<CAPTION>
                                                    June 30,
                                         -----------------------------
                                              1994              1995
                                         -----------------------------
     <S>                                 <C>               <C>
     Machinery and equipment             $ 6,621,985       $ 6,760,500
     Computer hardware and software        1,051,855         1,063,883
     Furniture and fixtures                  139,569           136,722
     Leasehold improvements               15,641,540        15,889,963
                                         -----------       -----------
                                          23,454,949        23,851,068
     Less accumulated depreciation
          and amortization                 6,986,188        10,229,685
                                         -----------       -----------
                                         $16,468,761       $13,621,383
                                         ===========       ===========
</TABLE>



Depreciation and amortization expense was $1,349,580, $2,043,537 and $3,284,583
for the years ended June 30, 1993, 1994 and 1995, respectively.

Maintenance and repair expense was approximately  $135,000, $229,000 and
$173,000 for fiscal years 1993, 1994 and 1995, respectively.




                                      33

<PAGE>   34

IMMUNOGEN, INC.
NOTES TO CONSOLIDATED FINANCIAL STATEMENTS, CONTINUED

F.  INCOME TAXES:

No income tax provision or benefit has been provided for U.S. federal income
tax purposes as the Company has incurred losses since inception.  As of June
30, 1995 net deferred tax assets totaled approximately $40.0 million consisting
of federal net operating loss carryforwards of approximately $102.0 million and
approximately $4.0 million of research and experimentation credit
carryforwards.  These net operating loss and credit carryforwards will expire
at various dates between 1996 and 2010 and may be subject to limitation when
used due to certain changes in ownership of the Company's capital stock.  Due
to the uncertainty surrounding the realization of these favorable tax
attributes in future tax returns, the net deferred tax assets of approximately
$38.0 million and $40.0 million at June 30, 1994 and June 30, 1995,
respectively, have been fully offset by a valuation allowance.  Income tax
expense consists primarily of state income taxes levied on the interest income
of the Company's wholly-owned subsidiary, ImmunoGen Securities Corp., at a rate
of 1.32%.

G.  CAPITAL STOCK:

  COMMON STOCK

On February 2, 1994 the Company sold 1,750,000 shares of common stock in a
public offering.  Proceeds to the company before deducting expenses amounted to
$12,250,000.  On February 8, 1994 as part of the same public offering, the
Underwriters exercised their over-allotment option to purchase an additional
262,500 shares of common stock.  Additional proceeds to the Company totaled
$1,837,500 before deducting offering expenses.

  STOCK OPTIONS

Under the Company's Restated Stock Option Plan (the "Stock Option Plan")
originally adopted by the Board of Directors on February 13, 1986, and
subsequently amended and restated, employees, consultants, and directors may be
granted options to purchase up to 2,400,000 shares of common stock of the
Company.  Prior to June 7, 1994, 1,700,000 shares of Common Stock  were
reserved for the grant of options under the Plan.  On June 7, 1994, the Board
of Directors authorized, and the shareholders subsequently approved, an
amendment to the Plan to increase the number of shares reserved for the grant
of options to 2,400,000 shares of Common Stock.


                                      34

<PAGE>   35
IMMUNOGEN, INC.
NOTES TO CONSOLIDATED FINANCIAL STATEMENTS, CONTINUED


<TABLE>
Information related to stock option activity under the Stock Option Plan during
fiscal years 1993, 1994 and 1995 is as follows.

<CAPTION>
                                                  Shares          Option Price
                                                ---------        --------------
      <S>                                       <C>              <C>
      Outstanding at June 30, 1992........        763,845        $0.67 - 14.75
                                                ---------        

      Granted.............................        647,000         6.75 - 12.00
      Exercised...........................        104,098         0.83 -  2.00
      Canceled............................         58,127         2.00 - 14.75
                                                ---------        
      Outstanding at June 30, 1993........      1,248,620         0.67 - 14.75
                                                ---------        

      Granted.............................        582,200         4.50 - 10.50
      Exercised...........................         41,438         0.90 -  2.00
      Canceled............................        205,869         2.00 - 14.75
                                                ---------        

      Outstanding at June 30, 1994........      1,583,513         0.67 - 14.75
                                                ---------        

      Granted.............................        338,300         1.94 -  4.38
      Exercised...........................         10,875         0.90 -  2.00
      Canceled............................        623,572         0.90 - 14.75
                                                ---------        

      Outstanding at June 30, 1995........      1,287,366        $0.67 - 14.75
                                                =========
</TABLE>


In addition to options granted under the Stock Option Plan, the Board
previously has approved the granting of other, non-qualified options.  In July
1987 and February 1988, the Company granted non-qualified options for the
purchase of 115,500 and 15,000 shares of common stock at exercise prices of
$0.67 and $0.90 per share, respectively.  During 1994 and 1995, options for
2,000  and 13,000 shares were exercised at a price of $0.67 per share.  As of
June 30, 1995, options for 19,687 of these shares had been canceled, 32,813 had
been exercised and 78,000 were outstanding and exercisable.

There are a total of 697,632 stock options exercisable under the Company's
stock option plans as of June 30, 1995.

Options vest at various rates over periods up to four years and may be
exercised within ten years from the date of grant.

  COMMON STOCK RESERVED

Shares of authorized common stock have been reserved for the exercise of all
options and warrants outstanding.

  WARRANTS

In connection with a capital lease financing in March 1994 the Company issued
warrants to purchase 26,738 shares of Common Stock at an exercise price of
$7.48 expiring in April 1999.  The value of these warrants, approximating
$77,000, is being recognized as interest expense over the life of the lease.


                                      35

<PAGE>   36
IMMUNOGEN, INC.
NOTES TO CONSOLIDATED FINANCIAL STATEMENTS, CONTINUED

H.  COMMITMENTS:

  OPERATING LEASES

At June 30, 1995 the Company is leasing facilities in Cambridge, Norwood and
Canton, Massachusetts.  The facilities are rented under four separate lease
arrangements whereby the respective lease terms expire in June 1997 (with a
three-year extension option), September 1997, June 2002 (with an option to
purchase at any time throughout the lease term) and April 2003.  The Company is
required to pay all operating expenses for the leased premises subject to
escalation charges for certain expense increases over a base amount.  Rent
expense for leased facilities and equipment was approximately $936,000,
$1,186,000 and $913,000 during fiscal years 1993, 1994 and 1995, respectively.


<TABLE>
The minimum rental commitments, including real estate taxes, for the next five
years under the lease agreements are as follows:

<CAPTION>
      Fiscal Year                            Amount
      -----------                            ------
         <S>                                <C>
         1996.............................. $1,023,814
         1997..............................  1,018,807
         1998..............................    673,929
         1999..............................    675,404
         2000..............................    668,702
</TABLE>


  CAPITAL LEASES

In fiscal year 1988, the Company, as part of one of its lease agreements,
arranged financing for $989,975 of improvements to one of its leased facilities
through the lessor.  The lessor obtained a five-year promissory note with a
bank specifically to finance the improvements to the facility.  The promissory
note was amortized over a ten-year period.  At the end of the first five years,
the lessor refinanced the unamortized principal due the bank.  Interest expense
on the new note is incurred at the rate of 7.50% per annum.

In fiscal 1993 the Company executed a sale/leaseback agreement to finance up to
$4.0 million of equipment costs at its Canton, Massachusetts manufacturing
facility.  In October 1993 the Company utilized $0.9 million of the agreement,
subsequently terminated this agreement and the outstanding  balance was repaid
in April 1994.

In March 1994 the Company executed a sale/leaseback agreement to finance
approximately $4.0 million of equipment at the Canton, Massachusetts
manufacturing facility.  As of June 30, 1994 all funds available under this
agreement had been received.  This transaction resulted in a gain on the sale
of the assets which has been deferred and included in other non-current
liabilities.  This deferred gain is being amortized as other income over the
life of the lease and amounted to approximately $56,000 in fiscal year 1995.
The transaction also included warrants which expire in April 1999 (see Note G).
The agreement commenced April 1, 1994 and expires in September 1998.

                                      36


<PAGE>   37
IMMUNOGEN, INC.
NOTES TO CONSOLIDATED FINANCIAL STATEMENTS, CONTINUED


<TABLE>
Assets recorded under capital leases as of June 30, 1994 and 1995 are included
in property and equipment as follows:
<CAPTION>
                                                June 30,
                                       ---------------------------
                                          1994             1995
                                       ---------------------------
  <S>                                  <C>              <C>
  Machinery and equipment............. $1,590,510       $1,590,510
  Leasehold improvements..............  3,414,793        3,413,490
  Less accumulated depreciation.......  1,032,880        1,727,403
                                       ----------       ----------

  Net book value...................... $3,972,423       $3,276,597
                                       ==========       ==========
</TABLE>


<TABLE>
The future minimum lease payments are as follows:

<CAPTION>
    Fiscal Year                                           Amount
    -----------                                         ----------
     <S>                                                <C>
     1996............................................   $1,309,270
     1997............................................    1,309,270
     1998............................................    1,196,674
     1999............................................      193,190
                                                        ----------

     Total future minimum lease payments.............    4,008,404
     Less amount representing interest...............      734,975
                                                        ----------
                                                
     Present value of minimum lease payments.........    3,273,429
     Less current Portion............................      942,749
                                                        ----------

     Noncurrent portion, minimum lease payments......   $2,330,680
                                                        ==========
</TABLE>


I.  RELATED PARTY TRANSACTION:

In April 1991 the Company made a $70,000 loan to one of its executive officers.
The note carried an interest rate of 8.75% and was payable in equal, biweekly
installments over a period of three years.  In December 1993, the loan was paid
in full.

J.  EMPLOYEE BENEFIT PLANS:

Effective September 1, 1990, the Company implemented a deferred compensation
plan under Section 401(k) of the Internal Revenue Code (the "Plan").  Under the
Plan, eligible employees are permitted to contribute, subject to certain
limitations, up to 15% of their gross salary.  The Company makes a matching
contribution which currently totals 20% of the employee's contribution, up to a
maximum amount equal to 1% of the employee's gross salary. In fiscal 1994 and
1995, the Company's contributions to the Plan amounted to $62,000 and $51,000,
respectively.



                                      37

<PAGE>   38

K.  SEVERANCE AGREEMENTS:

Two of the Company's senior executives terminated their employment in fiscal
1994.  At June 30, 1995 all severance costs had been paid to these individuals.




                                      38

<PAGE>   39

I
TEM 9.  CHANGES IN AND DISAGREEMENTS WITH ACCOUNTANTS ON ACCOUNTING AND
         FINANCIAL DISCLOSURE

None




                                      39

<PAGE>   40

PART III


ITEM 10. DIRECTORS AND EXECUTIVE OFFICERS

DIRECTORS

The section entitled "Election of Directors" in the Company's definitive proxy
statement for its 1995 Annual Meeting of Shareholders, which the Company
intends to file with the Securities and Exchange Commission on or about October
1, 1995, is hereby incorporated by reference.


<TABLE>
EXECUTIVE OFFICERS

The following is a list of the executive officers of the Company and their
positions with the Company. Each individual officer serves at the pleasure of
the Board of Directors.

<CAPTION>
Name                            Age     Positions with the Company
- ----                            ---     --------------------------
<S>                             <C>     <C>
Mitchel Sayare, Ph.D.           47      Chairman of the Board of Directors
                                        and Chief Executive Officer

Frank J. Pocher                 54      Vice President, Chief Financial
                                        Officer and Treasurer
                                
Walter A. Blattler, Ph.D.       46      Senior Vice President, Research and Development


Carol A. Gloff, Ph.D.           43      Vice President, Chief Regulatory Officer
</TABLE>


The background of these executive officers is as follows:

Mitchel Sayare, Chief Executive Officer and a Director since 1986, joined the
Company in 1986. He served as President from 1986 to July 1992. From 1982 to
1985, Mr. Sayare was an executive at Xenogen, Inc., a biotechnology company
specializing in monoclonal antibody-based diagnostic systems for cancer. As
Vice President for Development at Xenogen, Mr. Sayare was responsible for the
development of several diagnostic kits which were licensed to major
pharmaceutical companies. From 1977 to 1982, Mr. Sayare was Assistant Professor
of Biophysics and Biochemistry at the University of Connecticut. He holds a
Ph.D. in Biochemistry from Temple University School of Medicine.

Frank J. Pocher, Vice President, Chief Financial Officer and Treasurer joined
the Company in November 1988. Prior to joining ImmunoGen, Mr. Pocher was the
Executive Vice President and Chief Financial Officer of Seragen, Inc., a
biotechnology company developing recombinant products for cancer and
transplantation rejection. From 1980 to 1984, Mr. Pocher served as Chief
Financial Officer and then President and Chief Executive Officer of Aviation
Simulation Technology, Inc. Prior to that time, he held a variety of senior
financial positions at General Electric Company and Honeywell, Inc. He holds an
MBA from Rutgers University.

Walter A. Blattler, Ph.D., Senior Vice President, Research and Development,
joined the Company in October 1987. From 1981 to 1987, Dr. Blattler was chief
scientist for the ImmunoGen-supported research program at Dana-Farber 



                                      40

<PAGE>   41
Cancer Institute, where he managed the work of fourteen other scientists.
Dr. Blattler received his Ph.D. from the Swiss Federal Institute of Technology
in Zurich in 1978.

Carol A. Gloff, Ph.D., Vice President, Chief Regulatory Officer, joined the
Company in November 1993. Prior to joining ImmunoGen, Dr. Gloff held various
positions at Alkermes, Inc., a neuropharmaceutical company developing CNS
therapeutics and diagnostics, including Director of Product Development and
most recently Vice President of Regulatory Affairs. From 1984 to 1990, Dr.
Gloff held a variety of positions at Triton Biosciences, Inc., a biotechnology
firm specializing in recombinant DNA and monoclonal antibody-derived
technologies applied to cancer diagnosis and therapy, most recently as Manager
of Toxicology/Pharmacology. Prior to that time, Dr. Gloff held positions at
Pennwalt Pharmaceuticals and the University of Rochester Medical Center. Dr.
Gloff holds a Ph.D. in Pharmaceutical Chemistry from the University of
California San Francisco.

The section entitled "Compliance with Section 16(a) of the Securities Exchange
Act of 1934" in the Company's definitive proxy statement for its 1995 Annual
Meeting of Shareholders is hereby incorporated by reference.


ITEM 11. EXECUTIVE COMPENSATION

The reports entitled "Summary Compensation Table," "Option Grants in Last
Fiscal Year," "Employment Contracts, Termination of Employment and Change in
Control Agreements" and "Aggregated Option Exercises in Last Fiscal Year and
Fiscal Year-End Values" in the Company's definitive proxy statement for its
1995 Annual Meeting of Shareholders are hereby incorporated by reference.


ITEM 12. SECURITIES OWNERSHIP OF CERTAIN BENEFICIAL OWNERS AND MANAGEMENT

The section entitled "Principal Shareholders" in the Company's definitive proxy
statement for its 1995 Annual Meeting of Shareholders is hereby incorporated by
reference.


ITEM 13. CERTAIN RELATIONSHIPS AND RELATED TRANSACTIONS

The section entitled "Certain Transactions" in the Company's definitive proxy
statement for its 1995 Annual Meeting of Shareholders is hereby incorporated by
reference.



                                      41

<PAGE>   42

PART IV


ITEM 14. EXHIBITS, FINANCIAL STATEMENT SCHEDULES AND REPORTS ON FORM 8-K

         (a) Financial Statements

         (1) and (2) See "Index to Consolidated Financial Statements and 
Supplemental Schedules" at Item 8 of this Annual Report on Form 10-K. 
Schedules not included herein are omitted because they are not applicable or 
the required information appears in the Consolidated Financial Statements or 
Notes thereto.


<TABLE>
         (3) Exhibits
<CAPTION>
        Exhibit No.     Description
        -----------     -----------
         <S>            <C>
         (3.1)          Restated Articles of Organization+

         (3.2)          By-Laws, as amended#

         (4.1)          Article 4 of the Restated Articles of Organization (See Exhibit 3.1)+

         (4.2)          Form of Common Stock Certificate*

        (10.1)          Research and License Agreement dated as of May 22, 1981 by and 
                        between the Registrant and Sidney Farber Cancer Institute, Inc. (now 
                        Dana-Farber Cancer Institute, Inc.) with addenda dated as of August 13, 
                        1987 and August 22, 1989*

        (10.3)          Amended and Restated Registration Rights Agreement dated as of 
                        December 23, 1988 by and among the Registrant and various beneficial 
                        owners of the Registrant's securities*

        (10.4) x        Restated Stock Option Plan##

        (10.6) x        Letter Agreement Regarding Employment dated as of October 14, 1988 
                        between the Registrant and Mr. Frank J. Pocher*

        (10.7) x        Letter Agreement Regarding Employment dated as of October 1, 1987 
                        between the Registrant and Dr. Walter A. Blattler*

        (10.8a)x        Letter Agreement Regarding Employment Termination of Dr. Carol L. 
                        Epstein, dated April 16, 1994 as amended May 25 and June 6, 1994###

        (10.9)          Lease dated June 30, 1987 by and between Edward S. Stimpson, III and 
                        Harry F. Stimpson, III, as trustees, lessor, and the Registrant, lessee1

        (10.10)         Lease dated as of January 13, 1989 by and between FAR IV Limited        
                        Partnership, lessor, and the Registrant, lessee2
</TABLE>




                                      42

<PAGE>   43

<TABLE>
        <S>             <C>
        (10.10a)        First Amendment to Lease dated as of February 1, 1990 by and between 60 
                        Hamilton Street Limited Partnership, lessor, and Registrant, lessee3

        (10.11)         Leases dated as of December 1, 1986 and June 21, 1988 by and between      
                        James H. Mitchell, Trustee of New Providence Realty Trust, lessor, and 
                        Charles River Biotechnical Services, Inc. ("Lessee") together with
                        Assignment of Leases dated June 29, 1989 between Lessee and
                        the Registrant4

        (10.11a)        First Amendment, dated as of May 9, 1991, to Lease dated as of June 21, 
                        1988 by and between James A. Mitchell, Trustee of New Providence Realty 
                        Trust, lessor, and the Registrant5

        (10.13c)x       Letter Agreement Regarding Compensation of Mitchel Sayare, dated 
                        April 29, 1994###

        (10.14a)x       Transition Agreement Regarding Employment Termination of Dr. 
                        Donald J. McCarren, dated May 20, 1994###

        (10.15)         Lease dated as of July 1, 1992 by and between AEW#1 Corporation, 
                        lessor, and the Registrant, lessee++

        (10.16)         Lease dated as of December 23, 1992 by and between Massachusetts 
                        Institute of Technology, lessor, and the Registrant, lessee##

        (10.18)         Option Agreement dated April 5, 1990 by and between the Registrant 
                        and Takeda Chemical Industries, Ltd.6

        (10.19a)x       Separation Agreement regarding employment termination of Robert E. 
                        Tellis dated June 14, 1994 and as amended June 21, 1994###

        (10.21) x       Letter Agreement Regarding Employment dated September 15, 1993 between 
                        the Registrant and Carol A. Gloff###

        (10.22)         Capital Lease Agreement dated March 31, 1994 by and between the Registrant 
                        and Aberlyn Capital Management Limited Partnership###

        (10.23)         Sublease dated as of August 31, 1995 by and between the Registrant, as 
                        landlord, and Astra Research Center Boston, Inc., as tenant

        (10.24)         Equipment Use and Services Agreement dated as of August 31, 1995 by and 
                        between the Registrant, as landlord, and Astra Research Center Boston, 
                        Inc., as tenant

        (10.25)         Consent to Sublease and Agreement dated as of August 31, 1995 by and 
                        between Massachusetts Institute of Technology, as lessor, the Registrant, 
                        as sublessor, and Astra Research Center Boston, Inc., as sublessee
</TABLE>




                                      43

<PAGE>   44


<TABLE>
        <S>             <C>
        (10.26)         Amendment to Lease dated August 31, 1995 between Massachusetts Institute 
                        of Technology, as lessor, and the Registrant, as lessee

        (10.27)         Form of 7% Subordinated Convertible Debenture Due July 31, 1996 and 
                        Schedule of Debenture Holders

        (10.28)         Form of Offshore Securities Subscription Agreement between the Registrant 
                        and Purchasers of the Debentures.

        (21)            Subsidiaries of the Registrant

        (23)            Consent of Coopers & Lybrand.
<FN>
  * Previously filed with the Commission as Exhibits to, and incorporated
    herein by reference from, the Registrant's Registration Statement on Form S-1,
    File No. 33-31219.

  + Previously filed with the Commission as Exhibits to, and incorporated
    herein by reference from, the Registrant's Registration Statement on Form S-1,
    File No. 33-38883.

 ++ Previously filed with the Commission as Exhibits to, and incorporated
    herein by reference from, the Registrant's annual report on Form 10-K for the
    fiscal year ended June 30, 1992.

  # Previously filed with the Commission as Exhibits to, and incorporated
    herein by reference from, the Registrant's annual report on Form 10-K for the
    fiscal year ended June 30, 1990.

 ## Previously filed with the Commission as Exhibits to, and incorporated
    herein by reference from, the Registrant's quarterly report on Form 10-Q for
    the quarter ended December 31, 1992.

### Previously filed with the Commission as Exhibits to, and
    incorporated herein by reference from the registrant's annual report on Form
    10-K in the fiscal year ended June 30, 1994.

  1 Previously filed with the Commission as Exhibit No. 10.8 to, and
    incorporated herein by reference from, the Registrant's Registration Statement
    on Form S-1, File No. 33-31219.

  2 Previously filed with the Commission as Exhibit No. 10.9 to, and
    incorporated herein by reference from, the Registrant's Registration Statement
    on Form S-1, File No. 33-31219.

  3 Previously filed with the Commission as Exhibit No. 10.9a to, and
    incorporated herein by reference from, the Registrant's Registration Statement
    on Form S-1, File No. 33-38883.

  4 Previously filed with the Commission as Exhibit No. 10.10 to, and
    incorporated herein by reference from, the Registrant's Registration Statement
    on Form S-1, File No. 33-31219.

  5 Previously filed with the Commission as Exhibit No. 10.10a to, and
    incorporated herein by reference from, the Registrant's Registration Statement
    on Form S-1, File No. 33-43725, as amended.
</TABLE>




                                      44

<PAGE>   45
  6 Previously filed with the Commission as Exhibit No. 10.15 to, and
    incorporated herein by reference from, the Registrant's Registration 
    Statement on Form S-1, File No. 33-38883.

  x Exhibit is a management contract or compensatory plan, contract or
    arrangement required to be filed as an exhibit to Form 10-K.

        (b) Reports on Form 8-K.
        
            No reports on Form 8-K were filed during the quarter 
            ended June 30, 1995.



                                      45

<PAGE>   46

Signatures

Pursuant to the requirements of Section 13 or 15(d) of the Securities and
Exchange Act of 1934, the Registrant has duly caused this report to be signed
on its behalf by the undersigned, thereunto duly authorized.

IMMUNOGEN, INC.

By:                /s/Mitchel Sayare
                   -----------------
                   Mitchel Sayare
                   Chairman of the Board and
                   Chief Executive Officer

Dated:  September 28, 1995

Pursuant to the requirements of the Securities and Exchange Act of 1934, this
report has been signed below by the following persons on behalf of the
Registrant in the capacities and on the dates indicated.


<TABLE>
<CAPTION>
Signature                           Title                               Date
- ----------------------------------------------------------------------------------
<S>                           <C>                               <C>
/s/ Mitchel Sayare            Chairman of the Board of          September 28, 1995
- ------------------            Directors and Chief
Mitchel Sayare                Executive Officer
                              (principal executive officer)


/s/ Frank J. Pocher           Vice President, Chief             September 28, 1995
- ------------------            Financial Officer and
Frank J. Pocher               Treasurer (principal
                              financial officer and
                              principal accounting
                              officer)


/s/ Michael Eisenson          Director                          September 28, 1995
- --------------------
Michael Eisenson


/s/ Stuart F. Feiner          Director                          September 28, 1995
- --------------------
Stuart F. Feiner


/s/ Donald E. O'Neill         Director                          September 28, 1995
- ---------------------
Donald E. O'Neill

</TABLE>




                                      46

<PAGE>   47

<TABLE>

INDEX TO EXHIBITS

<CAPTION>
Exhibit
No.                 Description                                               
- -------             -----------                                               
<S>                 <C>                                                       
10.23               Sublease dated as of August 31, 1995 by and               
                    between the Registrant, as landlord, and                  
                    Astra Research Center Boston, Inc., as tenant             
                                                                              
10.24               Equipment Use and Services Agreement dated                
                    as of August 31, 1995 by and between the                  
                    Registrant, as landlord, and Astra Research               
                    Center Boston, Inc., as tenant                            
                                                                              
10.25               Consent to Sublease and Agreement dated                   
                    as of August 31, 1995 by and between                      
                    Massachusetts Institute of Technology, as lessor,         
                    the Registrant, as sublessor, and Astra Research          
                    Center Boston, Inc., as sublessee                         
                                                                              
10.26               Amendment to Lease dated August 31, 1995                  
                    between Massachusetts Institute of Technology,            
                    as lessor, and the Registrant, as lessee                  
                                                                              
10.27               Form of 7% Subordinated Convertible Debenture             
                    Due July 31, 1996 and Schedule of Debenture Holders       
                                                                              
10.28               Form of Offshore Securities Subscription                  
                    Agreement between the Registrant and                      
                    Purchasers of the Debentures                              
                                                                              
21                  Subsidiaries of the Registrant                            
                                                                              
23                  Consent of Coopers & Lybrand                              
</TABLE>





                                      47





<PAGE>   1

                                   SUBLEASE
Dated: August 31 , 1995

                            PRELIMINARY STATEMENT
                            ---------------------

     By a Lease (the "Main Lease"), MASSACHUSETTS INSTITUTE OF TECHNOLOGY
("Overlandlord") leased to Landlord the building known as and numbered 128
Sidney Street, Cambridge, Massachusetts, containing approximately 37,700
rentable square feet in all (the "Main Premises"). The Initial Lease Term of
the Main Lease commenced on December 23, 1992, and will expire on             , 
2003. Landlord desires to sublease to Tenant a portion of the Main Premises
as hereinafter described, and on the terms and conditions hereinafter set
forth.

1.0  PARTIES AND PREMISES.  IMMUNOGEN, INC. ("Landlord") hereby
     SUBLEASES unto ASTRA RESEARCH CENTER BOSTON, INC. a Massachusetts
     corporation ("Tenant"), the following premises:

          A portion of the building known as and numbered 128 Sidney
          Street, Cambridge, Massachusetts (the "Building"), which portion
          contains approximately 30,778 rentable square feet (consisting of
          30,309 square of office and laboratory space and 469 square feet of
          shipping area), and which comprises the entire Building other than
          the portion shown on Exhibit A, which portion will be retained by
          Landlord for its use. The Building is located on the parcel of land
          (the "Land") shown on the plan attached
 hereto as Exhibit B, together
          with the portion(s) of the parking area located on the Land as are
          hereafter designated by Landlord and Tenant pursuant to Section 9.1
          below (collectively, the "Leased Land") (such portion of the Building
          being sometimes hereinafter referred to as the "Premises"),

     together with the benefit of, and subject to (as the case may
     be) all rights, easements, covenants, conditions, encumbrances,
     encroachments and restrictions now or hereafter affecting the Building or
     the Premises. Overlandlord has the right under the Main Lease, without the
     necessity of obtaining Landlord's or Tenant's consent thereto or joinder
     therein, to grant, permit, or enter into during the term of this Sublease
     such additional rights, easements, covenants, conditions, encumbrances,
     encroachments and restrictions with respect to the Land as Overlandlord
     may deem appropriate, provided that, pursuant to the Main Lease, no such
     rights, easements, covenants, conditions, encumbrances, encroachments or
     restrictions shall materially affect Tenant's use of the Premises for the
     Permitted Uses hereunder, to the extent that Tenant's use of the Premises
     is consistent with Landlord's use under the Main Lease.

2.0  LEASE TERM; COMMENCEMENT DATE; EXTENSION OPTION.

     2.1  LEASE TERM; COMMENCEMENT DATE.  The initial term of
          this Sublease (the "Initial Term") shall commence on September 1,
          1995 (the "Commencement Date") and shall expire, unless sooner
          terminated as hereinafter provided, at 11:59 p.m. on February 28,
          1997.

     2.2  EXTENSION OPTIONS.  (a) Provided that, at the time of such
     exercise, (i) there exists no Event of Default; (ii) this Sublease is
     still in full force and effect; and (iii) Tenant shall not have assigned
     this Sublease or sublet any or all of the Premises, Tenant shall have the
     right to extend the Term of this Lease for two extended terms (the "First
     Extended Term" and the "Second Extended Term") of one (1) year each. The
     First Extended Term shall commence on March 1, 


                                      49

<PAGE>   2

     1997, and shall end on February 28, 1998, and the Second Extended Term 
     shall commence on March 1, 1998, and shall end on February 28, 1999. Tenant
     shall exercise each such option by giving Landlord notice of its desire to
     do so, not later than (i) December 15, 1995 with respect to the First
     Extended Term, and (ii) June 30, 1996 with respect to the Second Extended
     Term, it being agreed that time shall be of the essence with respect to the
     giving of each such notice. The giving of any such notice shall    
     automatically extend the term of this Sublease for the applicable Extended
     Term, and no instrument of renewal need be executed. In the event that
     Tenant fails to give such notice to Landlord, the term of this Lease shall
     automatically terminate at the end of the term then in effect, and Tenant
     shall have no further right or option to extend the term of this Sublease.
     Each Extended Term shall be on all the terms and conditions of this Lease,
     except that the Rent for each Extended Term shall be determined in
     accordance with Section 3.1. As used in this Sublease, "Lease Term" shall
     mean, collectively, the Initial Term and, if Tenant duly exercises either
     extension option, then the applicable Extended Term.

3.0  RENT; NET LEASE

     3.1        DEFINITIONS; PAYMENT OF RENT.  Tenant shall pay Landlord, 
                without offset or deduction and without previous demand 
                therefor, as items constituting rent (collectively, "Rent"):

                (a)    Rent at the following rates:
                       (i)   for each Lease Year of the Initial Term, $19.50 
                             per rentable square foot of Premises per Lease
                             Year;
               
                       (ii)  for each Lease Year during the First Extended Term,
                             an amount equal to the product of (x) the Rent
                             payable with respect to the Initial Term,
                             multiplied by (y) a fraction, the numerator of
                             which is the point at which the "Index" (as
                             hereinafter defined) stood at the last day of the
                             Initial Term, and the denominator of which is the
                             point at which the Index stood at the date hereof.

                       (iii) for each Lease Year during the Second Extended 
                             Term, an amount equal to the sum of: (A) the
                             product of (x) the Rent payable with respect to the
                             First Extended Term, multiplied by (y) a fraction,
                             the numerator of which is the point at which the
                             Index stood at the last day of the First
                             Extended Term, and the denominator of which is the
                             point at which the Index stood at the first day of
                             the First Extended Term; plus (B) $2.00 per
                             rentable square foot contained in the Premises.
                
                (b)    For purposes hereof, the term "Index" shall mean
                       the United States Department of Labor Consumer Price
                       Index forUrban Consumers, Boston, MA, All Items,
                       1982-84=100 (CPI-U). As of July 31, 1995, the CPI-U was
                       157.8.

                Basic Rent shall be due and payable in equal monthly
                installments, in advance, commencing on the date hereof, and    
                continuing thereafter on the first day of each calendar month or
                portion thereof during the Lease Term.  Basic Rent shall be
                pro-rated for partial months occurring at the beginning or the
                end of the Lease Term; and
          
                (c)    All other costs, charges, or expenses which Tenant in 
                       this Sublease agrees to pay, or which Landlord pays or   
                       incurs as the result of a default by Tenant 



                                      50

<PAGE>   3

                       hereunder, including any penalty or interest which may be
                       added for nonpayment or late payment thereof as
                       provided in this Sublease (collectively, "Additional
                       Rent").

                As used in this Sublease, "Lease Year" means the twelve (12)
                month period commencing on September 1, 1995, and each
                successive twelve (12) month period included in the Lease Term
                commencing on an anniversary of that day, but if the expiration
                of the Lease Term or the earlier termination of the Lease
                does not coincide with the termination of such a twelve (12)
                month period, the term "Lease Year" shall mean the portion of
                such twelve (12) month period before such expiration or
                termination.
          
                All payments shall be made to Landlord at such place as Landlord
                shall, from time to time, in writing designate, the     
                following being now so designated:

                       ImmunoGen, Inc.
                       128 Sidney Street
                       Cambridge, MA 02139
                       Attention:  Mr. Frank Pocher

3.2  RENT COMMENCEMENT DATES.  Tenant's obligation under this Sublease to
     pay Rent shall commence on September 1, 1995. Notwithstanding the
     foregoing, the Rent for the month of September, 1995 shall be paid on
     execution hereof.

3.4  NET LEASE.  It is the intention of the Landlord and the Tenant that
     this is a "net" lease and that the Rent herein specified shall be paid to
     the Landlord in each month during the Lease Term, and that all costs,
     expenses, and obligations of every kind relating to the Premises whether
     usual or unusual, ordinary or extraordinary, foreseen or unforeseen, which
     may arise or become due during the Lease Term, shall be paid by Tenant
     except as otherwise specifically provided herein.
     
4.0  PERMITTED USE.  The Premises shall be occupied by Tenant and used for
     the following purposes (the "Permitted Uses") only and for no other:
     Research laboratory, manufacturing and accessory and office uses, to the
     extent permitted (either as a matter of right or pursuant to a duly-issued
     special permit) under the Zoning Ordinance of the City of Cambridge, as
     amended from time to time.

     If Tenant elects to use the Premises for a research laboratory,
     manufacturing or office use which requires a special permit from a
     governmental authority, Overlandlord has agreed under the Main Lease, and
     Landlord hereby agrees, to join in applying therefor, provided that (i)
     such application shall be made and prosecuted solely at Tenant's cost and
     expense, (ii) Tenant shall promptly reimburse Overlandlord and Landlord
     for all out of pocket expenses reasonably incurred by them in connection
     with such application, (iii) Tenant shall keep Overlandlord and Landlord
     informed of the status thereof, including providing reasonable advance
     notice of all hearings and working sessions involving governmental
     representatives, which hearings and working sessions Overlandlord and
     Landlord shall be entitled to attend, and (iv) such special permit shall
     be issued subject only to such conditions (if any) as are reasonably
     acceptable to Overlandlord and Landlord.
     


                                      51

<PAGE>   4


5.0  TAXES.

     5.1  TAXES.  Tenant shall pay as Additional Rent 82.5% of all
          taxes, special or general assessments, water rents, betterments,
          rates and charges, sewer rents and other impositions and charges
          imposed by Overlandlord on Landlord under the terms and conditions of
          the Main Lease during the Lease Term, as well as any tax based on a
          percentage fraction or capitalized value of the Rent (whether in lieu
          of or in addition to the taxes hereinbefore described) (collectively,
          "Taxes"). Notwithstanding the foregoing, with respect to betterments
          imposed upon Landlord under the Main Lease, Tenant shall be
          responsible only for that portion of such betterment as relates to
          the Lease Term, which shall be computed on a "straight-line" basis.

     5.2  PAYMENT OF TAXES.  Landlord shall use its best efforts to
          send copies of all bills for Taxes to Tenant within ten (10) days of
          Landlord's receipt thereof.  Tenant shall pay to Landlord, as
          Additional Rent, 82.5% ("Tenant's Tax Share") of all Taxes paid by
          Landlord to Overlandlord, as calculated in a manner consistent with
          Exhibit C attached to the Main Lease, within ten (10) days of
          Tenant's receipt of such copy of the bill. Provided that Tenant pays
          Tenant's Tax Share of Taxes to Landlord within the time provided in
          this Section 5.2, Landlord shall pay the Taxes to Overlandlord in a
          timely manner under the Main Lease. Tenant's obligations under this
          Section 5 shall be pro-rated for partial tax years at the beginning
          or end of the Lease Term.

     5.3  ABATEMENT OF TAXES.  Pursuant to Main Lease, Landlord may
          from time to time apply for an abatement or other reduction in the
          amount of Taxes due under the Main Lease. In the event that Landlord
          elects for any reason not to seek and abatement or reduction for any
          fiscal year for which Tenant has paid or will pay a portion of Taxes,
          Landlord shall so advise Tenant, not later than seven (7) business
          days prior to the date on which applications are due, and (provided
          that Overlandlord does not file any such application) Tenant may
          thereafter file an application in its own name. If either party files
          such an application, it shall thereafter pursue the same at its own
          cost and expense, and shall at all times keep the other party
          informed as to the status thereof and, if requested, provide the
          other party with copies of relevant documentation. Neither party
          shall in any event discontinue a pending application without giving
          the other party reasonable advance notice thereof and affording the
          other party a reasonable opportunity to substitute itself for the
          discontinuing party. If and to the extent that either party actually
          receives any refunds or abatements on account of Taxes, all or any
          portion of which was paid by the other party hereunder, then upon
          such receipt, the party obtaining the same shall pay to the other
          party (provided that, in the case of a payment due Tenant, there then
          exists no Event of Default), an amount equal to the other party's
          share of such refund or abatement (net of any expense or cost
          incurred in obtaining the same).

6.0  UTILITIES AND SERVICES.  Landlord and Tenant shall share utilities,
     such as electricity, natural gas, water and property damage insurance
     charges, with Tenant being responsible for ninety percent (90%) of the
     cost thereof, and Landlord being responsible for ten percent (10%) of the
     cost thereof. Landlord and Tenant shall each pay for their own telephone
     service. The water and sewer service for the Premises shall remain in the
     name of Overlandlord, and those licenses or permits relating to the
     Premises which are required by applicable laws, codes, ordinances, rules
     or regulations to remain in Landlord's name (including, without
     limitation, those relating to the backflow preventers now or hereafter
     installed in the Building) shall remain in the name of 



                                      52

<PAGE>   5

     Overlandlord, but Landlord and Tenant shall be responsible for the payment
     of charges therefor, as hereinabove provided, which charges Tenant shall
     pay to Landlord, as Additional Rent, within fifteen (15) days of Landlord's
     receipt from Overlandlord of a demand for such payment together with a copy
     of the applicable bill. As provided in the Main Lease, in no event shall
     Overlandlord be responsible for charges for any utilities or services
     consumed by Landlord or Tenant or provided to Tenant at the Premises.

7.0  INSURANCE

     7.1  PUBLIC LIABILITY INSURANCE.  Tenant shall take out and
          maintain in force throughout the Lease Term comprehensive public
          liability insurance, written on an occurrence basis, naming
          Overlandlord, Landlord, Tenant, and persons claiming under them, if
          any, as additional insureds against all claims and demands for any
          injury to persons or property which may be claimed to have occurred
          in, on or about the Premises or ways adjoining the Premises, in an
          amount which at the beginning of the Lease Term shall not be less
          than $5,000,000 for bodily injury, personal injury, death and
          property damage, combined single limit, or such higher amounts as
          Overlandlord shall reasonably determine are required by reason of
          Tenant's use of the Premises, and which thereafter, if Overlandlord
          requires, shall be in such higher amounts as are then consistent with
          sound commercial practice in Cambridge, Massachusetts.

     7.2  CASUALTY INSURANCE.  As provided in the Main Lease,
          Landlord shall maintain throughout the Lease Term a policy of fire,
          vandalism, malicious mischief, extended coverage and so-called all
          risk coverage insurance insuring the Building. Tenant agrees to
          reimburse Landlord, as Additional Rent, for an amount equal to ninety
          percent (90%) of the premiums, costs and expenses incurred by
          Landlord for such insurance. Landlord shall use all reasonable
          efforts to have Tenant named as an additional insured party on such
          policy (provided that Tenant shall pay 100% of any additional premium
          arising therefrom). Tenant shall make such payments to Landlord, from
          time to time, within thirty (30) days after receipt of a copy of
          Landlord's statement, which shall be accompanied by a copy of the
          bill(s) from Landlord's insurer. Tenant shall not carry any insurance
          concurrent in coverage and contributing in the event of loss with any
          insurance required to be furnished by Landlord hereunder if the
          effect of such separate insurance would be to reduce the protection
          or the payment to be made under Landlord's insurance.
          
          All insurance policies maintained pursuant to this Section
          7.2 shall include insurance against payment of rents in an amount
          sufficient to pay all Rent which would otherwise be required to be
          paid under this Sublease during the period of restoration.
          
     7.3  CERTIFICATE OF INSURANCE.  All insurance required to be
          maintained by Tenant hereunder: shall be placed with insurers
          reasonably satisfactory to Landlord and authorized to do business in
          Massachusetts; shall provide that it may not be canceled without at
          least thirty (30) days prior written notice to each additional
          insured or certificate holder named therein; and shall provide that
          it may not be amended without at least fifteen (15) days prior
          written notice to each such person.  Tenant shall furnish to Landlord
          certificates of insurance for all insurance required to be maintained
          by Tenant under this Sublease, together with evidence satisfactory to
          Landlord of the payment of all premiums for such policies.  Tenant,
          at Landlord's request, shall also deliver such 



                                      53

<PAGE>   6

          certificates and evidence of payment to the holder of any mortgage
          affecting the Premises or any portion thereof.
          
     7.4  WAIVER OF SUBROGATION.  To the extent to which a waiver of
          subrogation clause is available, Landlord and Tenant shall obtain a
          provision in all insurance policies carried by such party covering
          the Premises, including but not limited to contents, fire and
          casualty insurance, expressly waiving any right on the part of the
          insurer against the other party and against Overlandlord. If extra
          cost is chargeable for such provision, then Tenant shall pay such
          extra charge.
          
     7.5  WAIVER OF RIGHTS.  All claims, causes of action and rights
          of recovery for any damage to or destruction of persons, property or
          business which shall occur on or about the Premises which result from
          any of the perils insured under any and all policies of insurance
          maintained by Landlord or Tenant, are waived by each party as against
          the other party, and the officers, directors, employees, contractors,
          servants and agents thereof, regardless of cause, including the
          negligence of the other party and its respective officers, directors,
          employees, contractors, servants and agents, but only to the extent
          of recovery, if any, under such policy or policies of insurance;
          provided, however, that this waiver shall be null and void to the
          extent that any such insurance shall be invalidated by reason of this
          waiver.

8.0  ASSIGNMENT AND SUBLETTING.  Tenant shall not mortgage, pledge,
     hypothecate, or assign this Sublease or sub-sublease the Premises or any
     portion thereof (which term shall be deemed to include any arrangement
     pursuant to which a third party is permitted by Tenant to occupy all or
     any portion of the Premises).

9.0  PARKING.

     9.1  PARKING.  Tenant shall have the right to use forty-seven
          (47) parking spaces in the surface parking lot located on the Land
          (the "Parking Area"), which spaces are located pursuant to the Main
          Lease.  Such parking spaces shall be designated for use by Tenant
          (but neither Overlandlord nor Landlord shall be responsible for
          policing the use thereof). Tenant acknowledges and agrees that the
          parking spaces along the fence on the southerly boundary of the Land
          are already designated for use by another tenant and are not
          available to Tenant.  Landlord hereby grants to Tenant, as
          appurtenant to the Premises, the right to use all access drives and
          curb cuts to and from the Parking Area for purposes of vehicular
          access to the Parking Area and the Building.
          
10.0 LATE PAYMENT OF RENT.  Tenant agrees that in the event that any
     payment of Basic Rent or Additional Rent shall remain unpaid at the close
     of business on (x) with respect to Basic Rent, the seventh (7th) business
     day after the same is due and payable hereunder, and (y) with respect to
     Additional Rent, the seventh (7th) business day after receipt of
     Landlord's invoice therefor, there shall become due to Landlord from
     Tenant, as Additional Rent and as compensation for Landlord's extra
     administrative costs in investigating the circumstances of late Rent, a
     late charge of five percent (5%) of the amount overdue.  The assessment or
     collection of such a charge shall not be deemed to be a waiver by Landlord
     of any default by Tenant arising out of such failure to pay Rent when due.


                                      54

<PAGE>   7

11.0 TENANT'S COVENANTS.  Tenant acknowledges that (except for latent and
     structural defects, not apparent upon a reasonably careful visual
     inspection) the Building is in good and satisfactory order, repair and
     condition, and covenants, at its sole cost and expense, during the Lease
     Term and such further time as Tenant holds any part of the Premises:

     (a)  to pay when due the Basic Rent and all Additional Rent, and
          all charges for utilities and services supplied to the Premises
          pursuant to agreements between Tenant and the appropriate utility
          company or provider of such services,

     (b)  to keep the Premises, including, without limitation, the
          Building systems (such as plumbing, heating, ventilation and air
          conditioning, and electrical), the non-structural components of the
          Building and window glass, (excluding the exterior skin of the
          Building, the columns and beams and other structural members of the
          Building, and the Parking Area), in as good order, repair and
          condition as the same are in as of the date of this Sublease,
          excepting only damage by fire or other casualty or taking which
          Tenant is not otherwise required by the terms of this Sublease to
          repair or restore, and reasonable wear and tear;

     (c)  not to injure, overload or deface the Premises, nor
          knowingly to suffer or commit any waste therein, nor to place a load
          upon any floor which exceeds the floor load which the floor was
          designed to carry, nor to connect any equipment or apparatus to any
          Building system which exceeds the capacity of such system, nor to
          permit on the Premises any auction sale or any inflammable fluids or
          chemicals which are not used, stored and disposed of in compliance
          with all laws, ordinances, codes, rules and regulations, and the
          provisions of any license, permit or other governmental consent or
          approval required for or applicable now or at any time during the
          Lease Term to the Premises of any portion thereof or Tenant's use
          thereof (collectively, "Legal Requirements"), nor to permit any
          nuisance or the emission from the Premises of any objectionable
          vibration, noise, or odor, nor to permit the use of the Premises for
          any purpose other than the Permitted Uses, nor any use thereof which
          is contrary to any Legal Requirements, or which is liable to
          invalidate any insurance on the Building or its contents, or liable
          to render necessary any alterations or additions to the Building;
          
     (d)  not to obstruct in any manner any portion of the sidewalks
          or approaches to the Building or any portion of the Parking Area;
          
     (e)  to comply with all Legal Requirements and all reasonable
          recommendations of Landlord's and Overlandlord's fire insurance
          rating organization now or hereafter in effect, to obtain and
          maintain in full force and effect all licenses, permits and
          governmental consents and approvals required by any Legal Requirement
          for the operation of Tenant's business in the Premises (without
          intending hereby to vary the provisions of Section 4.0 above), to
          keep the Premises equipped with all reasonable and necessary safety
          appliances, and to procure (and maintain in full force and effect)
          all licenses, permits and other governmental consents and approvals
          required by any Legal Requirement or by the provisions of any
          applicable insurance policy because of the use made of the Premises
          by Tenant, and, if requested by Landlord or Overlandlord, to make all
          repairs, alterations, replacements or additions so required in and to
          the Premises, and to cooperate with Landlord and Overlandlord in the
          obtaining and renewal by Landlord or Overlandlord of all licenses,
          permits and other governmental consents and approvals 


                                      55

<PAGE>   8


          with respect to the Premises which Landlord or Overlandlord is
          required by applicable laws, ordinances, codes, rules or regulations
          to obtain in its own name, provided, however, that Tenant shall not be
          required by this paragraph (e) to undertake any structural change,
          improvement or modification to the Building in order to effect such
          compliance, except to the extent that the requirement for the same
          arises from Tenant's use of the Premises (as distinguished from
          Landlord's Permitted Uses under the Main Lease); 

     (f)  not to make any alterations, renovations, improvements and/or 
          additions to the Premises (collectively, "Alterations"), without on
          each occasion obtaining prior written consent of Landlord and
          Overlandlord (to the extent required under the Main Lease), which
          consent may be withheld by Landlord in its reasonable discretion.
          Prior to commencing any Alterations, Tenant shall: secure all
          necessary licenses, permits and other governmental consents and
          approvals; obtain the written approval of Landlord and, when required
          by the Main Lease, of Overlandlord, as to the plans and specifications
          for such work; obtain the written approval of Overlandlord and
          Landlord as to the general contractor (not to be unreasonably
          withheld, delayed or conditioned by Landlord, provided that
          Overlandlord approves the same); cause each contractor and
          subcontractor to carry worker's compensation insurance in statutory
          amounts covering all of the contractor's and subcontractor's
          employees; and cause each general contractor (or each trade contractor
          if there is no general contractor) to carry comprehensive public
          liability insurance in amounts reasonably satisfactory to Overlandlord
          and Landlord (such insurance to be written by companies reasonably
          satisfactory to them and insuring Tenant, Landlord and Overlandlord as
          well as the contractors).  All Alterations (other than Tenant's
          removable personal property and trade fixtures) shall, at the option
          of Landlord and Overlandlord, remain part of the Premises and shall
          not be removed upon the expiration or earlier termination of the Lease
          Term except for those items which Landlord or Overlandlord designates
          for removal in a notice given to Tenant at the time that Tenant
          requests Landlord's approval of such Alteration. Tenant shall pay
          promptly when due the entire cost of such work. Tenant shall not cause
          or permit any liens for labor or materials performed or furnished in
          connection therewith to attach to the Land or the Building, and shall
          discharge or bond any such liens which may be filed or recorded within
          ten (10) days after the filing or recording thereof.  All such work
          shall be performed in a good and workmanlike manner and in compliance
          with all Legal Requirements and the provisions of all applicable
          insurance policies.  Promptly after the completion of any Alterations,
          Tenant shall provide an as-built plan (or, where appropriate in light
          of the nature or scope of the Alterations, an as-built sketch) thereof
          to Landlord.  Tenant shall indemnify and hold Landlord and
          Overlandlord harmless from and against any and all suits, demands,
          causes of action, claims, losses, debts, liabilities, damages,
          penalties or judgments, including, without limitation, reasonable
          attorneys' fees, arising from injury to any person or damage to any
          property occasioned by or growing out of such work performed prior to 
          the last day of the Lease Term, which indemnity shall survive the
          expiration or termination of this Sublease;
          
     (g)  to save Landlord and Overlandlord harmless and indemnified
          from any loss, cost and expense (including, without limitation,
          reasonable attorney's fees) arising out of or relating to: (i) a
          claim of injury to any person or damage to any property while on the
          Premises, if not due to the negligence or willful misconduct of
          Landlord, Overlandlord or their respective officers, agents,
          employees, servants or contractors, or the breach of 



                                      56

<PAGE>   9

          Landlord's obligations under this Sublease; or to (ii) a claim of
          injury to any person or damage to any property in the Parking Area or
          on the sidewalks or ways adjoining the Premises, to the extent
          occasioned by any omission, neglect or default of Tenant or of anyone
          claiming by, through, or under Tenant, or any officer, agent,
          employee, servant,    contractor or invitee of any of the foregoing. 
          The provisions of this clause (g) shall survive the expiration or
          termination of this Sublease with respect to any claim arising prior
          to the last day of the Lease Term;
          
     (h)  to permit Landlord, Overlandlord and their respective
          agents to examine the Premises at reasonable times (provided 24 hours
          notice is given to Tenant, except in case of emergency), and if
          either shall so elect (without hereby imposing any obligation on
          Landlord to do so), to permit Landlord or Overlandlord to make any
          repairs or additions they may deem necessary; and at Tenant's expense
          to remove any Alterations, signs, awnings, aerials or flagpoles, or
          the like, not consented to in writing; and to permit Landlord and/or
          Overlandlord to show the Premises to prospective purchasers and
          tenants (at reasonable times on reasonable advance notice to Tenant)
          and to keep affixed to any suitable part of the Premises, during the
          twelve (12) months preceding the expiration of the Lease Term,
          appropriate notices for letting or selling;
          
     (i)  that all merchandise, furniture, fixtures, effects and
          property of every kind of Tenant and of all persons claiming by,
          through or under Tenant which may be on the Premises from time to
          time (collectively, "Tenant's Property") shall be at the sole risk of
          Tenant, and neither Landlord nor Overlandlord shall be liable if the
          whole or any part thereof shall be destroyed or damaged by fire,
          water or otherwise, or by the leakage or bursting of water pipes,
          steam pipes, or other pipes, or by theft or from any other cause
          unless caused by the negligence or willful misconduct of Landlord or
          Overlandlord, respectively;
          
     (j)  to pay promptly when due, all taxes of any kind levied,
          imposed or assessed on Tenant's Property, which taxes shall be the
          sole obligation of Tenant, whether the same is assessed to Tenant or
          to any other person and whether the property on which such tax is
          levied, imposed or assessed shall be considered part of the Premises
          or personal property;
          
     (k)  by 5:00 p.m., local time, on the last day of the Lease Term
          (or the effective date of any earlier termination of this Sublease as
          herein provided), to remove all of Tenant's Property, and those
          Alterations designated for removal as provided in paragraph (f)
          above, whether the same be permanently affixed to the Premises or
          not, and to repair any damage caused by any such removal to the
          reasonable satisfaction of Landlord and Overlandlord; and peaceably
          to yield up the Premises clean and in good order, repair and
          condition (excepting only reasonable wear and tear, and damage by
          fire or other casualty or taking which (in the case of the early
          termination of this Sublease) Tenant is not otherwise required by the
          terms of this Sublease to repair or restore); and to deliver the keys
          to the Premises to Landlord.  Any of Tenant's Property or those
          Alterations designated for removal as provided in paragraph (f)
          above, which is not removed by such date shall be deemed abandoned
          and may be removed and disposed of by Landlord in such manner as
          Landlord may determine, and Tenant shall pay to Landlord on demand,
          as Additional Rent, the entire cost of such removal and disposition,
          together with the costs and expenses incurred by Landlord in making
          any incidental repairs and replacements to the Premises necessitated
          by Tenant's failure to remove Tenant's 


                                      57

<PAGE>   10

          Property or any of those Alterations designated for removal as
          provided in paragraph (f) above, as required herein or by any other
          failure of Tenant to comply with the terms of this Sublease, and for
          use and occupancy during the period after the expiration of the Lease
          Term and prior to Tenant's performance of its obligations under this
          clause (k).  Tenant hereby acknowledges that any failure or delay on
          Tenant's part in surrendering the Premises as above provided shall
          subject Landlord to   liability to Overlandlord and to the expense of
          performing such work and the risk of losing a successor subtenant;
          
     (l)  to pay Landlord's reasonable expenses (including without
          limitation any costs or expenses that Landlord may have to pay to
          Overlandlord), including reasonable attorneys' fees, incurred in
          enforcing any obligations of Tenant under this Sublease;
          
     (m)  not to generate, store or use any "Hazardous Materials" (as
          hereinafter defined) in or on the Premises except in compliance with
          any and all applicable Legal Requirements, or dispose of Hazardous
          Materials from the Premises to any other location, except a properly
          approved disposal facility and then only in compliance with any and
          all applicable Legal Requirements, nor permit any occupant of the
          Premises to do so.  As used in this Sublease, "Hazardous Materials"
          means and includes any chemical, substance, waste, material, gas or
          emission which is radioactive or is deemed hazardous, toxic, a
          pollutant, or a contaminant under any statute, ordinance, by-law,
          rule, regulation, executive order or other administrative order,
          judgment, decree, injunction or other judicial order of or by any
          governmental authority, now or hereafter in effect, relating to
          pollution or protection of human health or the environment.  By way
          of illustration and not limitation, "Hazardous Materials" includes
          "oil", "hazardous materials", "hazardous waste", and "hazardous
          substance" as defined in the Comprehensive Environmental Response,
          Compensation and Liability Act, 42 U.S.C. Section 9601 et seq., as
          amended, the Resource Conservation and Recovery Act of 1976, 42
          U.S.C. Section 6902 et seq., as amended, and the Toxic Substances
          Control Act, 15 U.S.C. Section 2601 et seq., as amended, the
          regulations promulgated thereunder, and Massachusetts General Laws,
          Chapter 21C and Chapter 21E and the regulations promulgated
          thereunder.  If, at any time during the Lease Term, any governmental
          authority requires testing to determine whether there has been any
          release of Hazardous Materials by Tenant, then Tenant shall reimburse
          Landlord upon demand, as Additional Rent, for the reasonable costs
          thereof. Tenant shall execute such affidavits as may be reasonably
          requested by Landlord from time to time, concerning Tenant's best
          knowledge and belief concerning the presence of Hazardous Materials
          in or on the Premises.  Tenant shall provide to Landlord copies of
          all applications and filings made by or on behalf of Tenant with any
          federal, state or local governmental authority having jurisdiction
          over Hazardous Materials, which identify any Hazardous Materials
          used, generated, stored, disposed of or transported to or from the
          Premises by Tenant. Landlord and Overlandlord each reserves the right
          to enter the Premises at reasonable times (provided twenty-four (24)
          hours' notice is given to Tenant, except in case of emergency) to
          inspect the same for Hazardous Materials. Tenant's obligations under
          this paragraph (m) shall include, if at any time during the Lease
          Term Tenant uses or stores radioactive materials on the Premises,
          compliance with all so-called "close-out" procedures of the Nuclear
          Regulatory Commission or other federal, state or local governmental
          authorities having jurisdiction over radioactive materials,
          regardless of whether or not such procedures are completed prior to
          the expiration or earlier termination of the Lease Term.  Tenant
          shall indemnify, defend, and hold harmless Landlord and Overlandlord,
          as well as the holder(s) of any mortgage(s) on 


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<PAGE>   11

          the Premises or any portion thereof, from and against any claim, cost,
          expense, liability, obligation or damage, including, without
          limitation, reasonable attorneys' fees and the cost of litigation,
          arising from or relating to the breach by Tenant of the provisions of
          this clause (m), and shall immediately discharge or cause to be
          discharged any lien imposed upon the Building or the Land in
          connection with any such claim.  The provisions of this clause (m)
          shall survive the expiration or termination of this Sublease; and
          
     (n)  not knowingly to permit any officer, agent, employee,
          servant, contractor or visitor of Tenant to violate any covenant or
          obligation of Tenant hereunder.

12.0 INTENTIONALLY OMITTED.

13.0 EMINENT DOMAIN AND CASUALTY. With respect to any taking or damage to
     the Premises or the Building, Tenant expressly acknowledges and agrees
     that Landlord shall have no repair responsibility or liability, and Tenant
     shall not look to Landlord for the same, except to the extent to which
     Landlord is expressly liable for the same under Section 13.5(b) of the
     Main Lease. However, Landlord agrees to use all reasonable efforts to
     enforce its rights and Overlandlord's obligations under the Main Lease in
     respect of any matter covered by this Article 13. Further, in the event
     that the Main Lease shall be terminated as a result of any taking, fire or
     other casualty or event described in Article 13 of the Main Lease, this
     Sublease shall similarly terminate immediately prior to the termination of
     the Main Lease, and Landlord shall have no liability or obligation to
     Tenant as a result of such termination.

     13.1 SUBSTANTIAL TAKING.  In the event that the Main Lease is
          terminated due to any exercise of the right of eminent domain or
          other lawful power in pursuance of any public or other authority
          during the Lease Term, then this Sublease shall terminate immediately
          prior to the termination of the Main Lease.
          
     13.2 PARTIAL TAKING.  In the event that a taking (other than a
          de minimus taking) occurs and this Sublease is not terminated
          pursuant to Section 13.1 above, then either Landlord or Tenant shall
          have the right to terminate this Sublease by giving the other party
          notice of its desire to do so, within 30 days after notice of such
          taking, such termination to be effective on the day preceding the
          date possession is taken by the taking authority. Rent and other
          charges hereunder shall be apportioned as of the effective date of
          such termination.
          
     13.3 AWARDS. Landlord reserves and excepts all rights to damage
          to the Premises and the leasehold hereby created, now accrued or
          hereafter accruing by reason of any exercise of eminent domain, or by
          reason of anything done in pursuance of any public or other
          authority, and by way of confirmation, Tenant grants to Landlord any
          and all of Tenant's rights to such damages and covenants to execute
          and deliver such further instruments of assignment thereof as
          Landlord may from time to time request.  Tenant shall be entitled
          only to such award, if any, as is specifically allocated by the
          taking authority to Tenant on account of relocation expenses as a
          result of such taking.
          
     13.4 SUBSTANTIAL CASUALTY.  If the Premises are damaged by fire
          or other casualty, Tenant shall promptly notify Landlord and
          Overlandlord thereof. If the Main Lease is terminated due to any fire
          or casualty during the Lease Term, then this Sublease shall terminate


                                      59

<PAGE>   12
          immediately prior to the termination of the Main Lease. Further, if
          within sixty (60) days after the occurrence of such fire or other
          casualty, Overlandlord reasonably determines that it will not be able
          to repair, restore or reconstruct the shell of the Building (i. e.,
          the exterior skin, roof, structural columns and beams of the
          Building) within five (5) months of the date on which Overlandlord
          commences such work (subject to extension by reason of "Force
          Majeure" (as defined in Section 22.0 of the Main Lease)), Landlord
          shall so notify Tenant and Tenant shall have the right, within twenty
          (20) days after its receipt of Landlord's notice, to terminate this
          Sublease on twenty (20) days' prior written notice. In the event that
          this Sublease is terminated pursuant to this Section 13.4: (i) Rent
          shall be abated, to the extent the Premises are unusable for the
          Permitted Uses, from and after the date of such damage to the date of
          such termination of this Sublease, and no further Rent shall accrue
          or be payable after the date of such termination; and (ii) Tenant
          shall turn over and assign to Landlord all insurance proceeds (and
          rights' to receive the same) relating to the Building.
          
     13.5 REPAIR AND RESTORATION. In the event of a taking which does
          not result in the termination of this Sublease pursuant to Section
          13.1 above, or a casualty which does not result in the termination of
          this Sublease pursuant to Section 13.4 above, the Premises shall be
          repaired and restored as provided in the Main Lease, except that
          Tenant shall be solely responsible for restoration of any Alterations
          made by Tenant.

          Neither Overlandlord nor Landlord shall be liable for any
          inconvenience or annoyance to Tenant or injury to the business of
          Tenant resulting in any way from such taking or damage or the repair
          thereof.  Rent shall be abated from and after the date of such taking
          or damage to the date on which the Premises are substantially
          completed, to the extent the Premises are unusable for the Permitted
          Uses, but the amount of such abatement shall not exceed the amount
          actually received by Landlord under the rental loss insurance policy
          required by Section 7.2 above.
          
          In the event that the Premises have not been substantially
          restored to such a condition that (except for than Tenant's
          Alterations and Tenant's Property), the Premises are usable by Tenant
          for Permitted Uses, within six (6) months after the date of such
          damage (which period shall be extended for any delays caused by the
          acts or omissions of Tenant, its employees, agents, contractors or
          servants), Tenant shall have the right to terminate this Sublease on
          at least twenty (20) days' prior written notice to Landlord, such
          notice to be given within twenty (20) days of the expiration of such
          6-month period.
          
     13.6 CASUALTY DURING LAST 6 MONTHS.  Notwithstanding anything to
          the contrary contained in this Sublease, in the event that a material
          portion of the Building is damaged by a fire or other casualty
          occurring during the last six (6) months of the Lease Term (including
          any Extended Term with respect to which Tenant shall theretofore have
          exercised its option to extend), either party may terminate this
          Sublease by giving written notice to the other within twenty (20)
          days of the occurrence of such damage.  If this Sublease is so
          terminated, Tenant shall turn over and assign to Landlord all
          insurance proceeds (and rights to receive the same) relating to the
          Building and any Alterations.
          


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<PAGE>   13



14.0 DEFAULTS; EVENTS OF DEFAULT; REMEDIES.

     14.1 DEFAULTS; EVENTS OF DEFAULT.  The following shall, if any
          requirement for notice or lapse of time or both has not been met,
          constitute defaults hereunder, and, if such requirements have been
          met, constitute "Events of Default" hereunder:

          (a)  The failure of Tenant to perform or observe any
               of Tenant's covenants or agreements hereunder concerning the
               payment of money for a period of five (5) days after written
               notice thereof, provided, however, that Tenant shall not be
               entitled to such notice if Landlord has given notice to Tenant
               of two or more previous such failures within a twelve-month
               period, in which event such failure shall constitute an Event of
               Default hereunder upon the expiration of five (5) days after
               such payment was due;

          (b)  The failure of Tenant to maintain any insurance
               required hereunder in full force and effect;

          (c)  The failure of Tenant to perform or observe any
               of Tenant's other covenants or agreements hereunder for a period
               of twenty (20) days after written notice thereof (provided that,
               in the case of defaults not reasonably curable in twenty (20)
               days through the exercise of reasonable diligence, such 20-day
               period shall be extended for so long as Tenant commences cure
               within such period and thereafter prosecutes such cure to
               completion continuously and with reasonable diligence);
               
          (d)  The failure of Tenant to perform or observe any
               of Tenant's covenants or agreements under that certain Equipment
               Use and Services Agreement of even date, between Landlord and
               Tenant, which failure concerns the payment of money and
               continues beyond any applicable notice and grace periods
               therein;
               
          (e)  if the leasehold hereby created shall be taken on
               execution, or by other process of law, and such taking is not
               vacated by a final order of a court of competent jurisdiction
               within sixty (60) days thereafter; or if any assignment shall be
               made of Tenant's property for the benefit of creditors; or if a
               receiver, guardian, conservator, trustee in bankruptcy or
               similar officer shall be appointed to take charge of all or any
               part of Tenant's property by a court of competent jurisdiction,
               and such appointment is not vacated by a final order of a court
               of competent jurisdiction within sixty (60) days thereafter; or
               if a petition is filed by Tenant under any bankruptcy or
               insolvency law; or if a petition is filed against Tenant under
               any bankruptcy or insolvency law and the same shall not be
               dismissed within sixty (60) days from the date upon which it is
               filed; or if a lien or other involuntary encumbrance is filed
               against Tenant's leasehold (or against the Premises based on a
               claim against Tenant) and is not discharged or bonded within ten
               (10) days after the filing thereof.

     14.2 TERMINATION.  If an Event of Default shall occur, Landlord
          may, at its option, immediately or any time thereafter and without
          demand or notice, enter upon the Premises or any part thereof in the
          name of the whole and repossess the same as of Landlord's former
          estate and dispossess Tenant and those claiming through or under
          


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<PAGE>   14
          Tenant and remove their effects, without being deemed guilty of any
          manner of trespass and without prejudice to any remedies which might
          otherwise be used for arrears of rent or preceding breach of
          covenant, and upon such entry this Sublease shall terminate.  In lieu
          of making such entry, Landlord may terminate this Sublease upon ten
          (10) days' prior written notice to Tenant.  Upon any termination of
          this Sublease as the result of an Event of Default, Tenant shall quit
          and peacefully surrender the Premises to Landlord.
          
     14.3 SURVIVAL OF COVENANTS.  No such termination of this
          Sublease shall relieve Tenant of its liability and obligations under
          this Sublease and such liability and obligations shall survive any
          such termination.  Tenant shall indemnify and hold Landlord harmless
          from all loss, cost, expense, damage or liability arising out of or
          in connection with such termination.
          
          In the event of any such termination, Tenant shall pay to
          Landlord the Rent up to the time of such termination.  Tenant shall
          remain liable for, and shall pay on the days originally fixed for
          such payment hereunder, the full amount of all Basic Rent and
          Additional Rent as if this Sublease had not been terminated;
          provided, however, if Landlord relets the Premises, there shall be
          credited against such obligation the amount actually received by
          Landlord each month from such lessee after first deducting all costs
          and expenses (including without limitation attorneys' fees and costs)
          incurred by Landlord in connection with repossessing and reletting
          the Premises.

          At any time after such termination, and regardless of
          whether Tenant has made any payments to Landlord pursuant to the
          preceding paragraph of this Section, Landlord may demand and Tenant
          agrees to pay to Landlord on such demand, as and for liquidated and
          agreed damages for Tenant's default, the present value of the amount
          by which the aggregate Rent which would have been payable under this
          Sublease by Tenant from the date of such termination until what would
          have been the last day of the Lease Term but for such termination,
          exceeds the fair and reasonable rental value of the Premises for the
          same period, less Landlord's reasonable estimate of expenses to be
          incurred in connection with reletting the Premises, including,
          without limitation, all repossession costs, brokerage commissions,
          legal expenses, reasonable attorneys' fees and expenses of
          preparation for such reletting.
          
          In the event of the filing of a petition by or against
          Tenant under any federal bankruptcy or insolvency law now or
          hereafter in effect, nothing herein contained shall limit or
          prejudice the right of Landlord to prove and obtain as liquidated
          damages by reason of such termination, an amount equal to the maximum
          allowed by any statute or rule of law in effect at the time when, and
          governing the proceedings in which, such damages are to be proved,
          whether or not such amount be greater, equal to, or less than the
          amount of the difference referred to above.
          
     14.4 RIGHT TO RELET.  At any time or from time to time after any
          such termination, Landlord may relet the Premises or any part thereof
          for such a term (which may be greater or less than the period which
          would otherwise have constituted the balance of the Lease Term) and
          on such conditions (which may include concessions or free rent) as
          Landlord, in its reasonable discretion, may determine, and may
          collect and receive the rents therefor.  Landlord shall in no way be
          responsible or liable for any failure to relet the Premises or any
          part thereof, or for any failure to collect any rent due upon any
          such reletting.
          


                                      62

<PAGE>   15
     14.5 RIGHT TO EQUITABLE RELIEF.  In the event there shall occur
          a default or threatened default hereunder, Landlord shall be entitled
          to seek to enjoin such default or threatened default and shall have
          the right to invoke any right and remedy allowed at law or in equity
          or by statute or otherwise as though re-entry and other remedies were
          not provided for in this Sublease.
          
     14.6 RIGHT TO CURE. In the event of the occurrence of an Event
          of Default hereunder, Landlord or Overlandlord shall have the right
          to perform such defaulted obligation of Tenant, including the right
          to enter upon the Premises to do so. In the event of a default by
          Tenant hereunder which has not yet continued beyond the expiration of
          the applicable grace period but which Landlord determines constitutes
          an emergency threatening imminent injury to persons or damage to
          property, Landlord or Overlandlord shall have the right to perform
          such defaulted obligation of Tenant after giving Tenant such notice
          (if any) as is reasonable under the circumstances.  In either event,
          the aggregate of (i) all sums so paid by Landlord or Overlandlord, as
          the case may be, (ii) interest at the rate of the "prime" rate from
          time to time thereafter published in The Wall Street Journal plus
          1-1/2% per annum, or the highest rate permitted by law, whichever is
          less, on such sum, and (iii) all necessary incidental costs and
          expenses in connection with the performance of any such act by
          Landlord or Overlandlord, shall be deemed to be Additional Rent under
          this Sublease and shall be payable immediately upon demand. Landlord
          or Overlandlord may exercise its rights under this Section 14.6
          without waiving any other of Landlord's rights or releasing Tenant
          from any of its obligations under this Sublease.
          
     14.7 FURTHER REMEDIES.  Nothing in this Sublease contained shall
          require Landlord to elect any remedy for a default or Event of
          Default by Tenant hereunder, and all rights herein provided shall be
          cumulative with one another and with any other rights and remedies
          which Landlord may have at law or in equity in the case of such a
          default or Event of Default.

15.0 REAL ESTATE BROKER.  Landlord and Tenant each represent to the other
     that they have dealt with no broker (other than Fallon, Hines & O'Connor)
     in connection with this Sublease. Tenant agrees to indemnify and hold
     Landlord harmless from and against any claims for commissions or fees by
     any person (other than Fallon, Hines & O'Connor) claiming to have dealt
     with Tenant in connection with this Sublease. Landlord agrees to indemnify
     and hold Tenant harmless from and against any claims for commissions or
     fees by any person claiming to have dealt with Landlord in connection with
     this Sublease. Landlord shall be responsible for payment of any
     commissions due Fallon, Hines & O'Connor as a result of this Sublease.
     
16.0 NOTICES.  Whenever by the terms of this Sublease notice, demand, or
     other communication shall or may be given either to Landlord or to Tenant,
     the same shall be in writing and shall be sent by hand, or by registered
     or certified mail, postage prepaid, or by Federal Express or other similar
     overnight delivery service:

     Overlandlord:      Massachusetts Institute of Technology
                        Suite 200
                        238 Main Street
                        Cambridge, Massachusetts 02142
                        Attention:   Philip A. Trussell,
                                     Director of Real Estate
          


                                      63

<PAGE>   16

     with a copy to:    Peter Friedenberg, Esquire
                        Rackemann, Sawyer & Brewster
                        One Financial Center
                        Boston, Massachusetts 02111

     Landlord:          ImmunoGen, Inc.
                        148 Sidney Street
                        Cambridge, Massachusetts 02139
                        Attention:  Frank J. Pocher,
                        Chief Financial Officer

     with a copy to:    Stephen T. Langer, Esquire
                        Mintz, Levin, Cohn, Ferris, Glovsky & Popeo
                        One Financial Center
                        Boston, Massachusetts 02111

     Tenant:            ASTRA Research Center Boston, Inc.
                        128 Sidney Street
                        Cambridge, Massachusetts 02139
                        Attention: Hans G. Nilsson

     with a copy to:    Neal C. Tully, Esq.
                        Masterman, Culbert & Tully
                        One Lewis Wharf
                        Boston, MA 02110

     and to:            Stefan Oscarsson
                        Astra Hassle, AB
                        43183 Molndal,
                        Sweden

     Any notice, demand or other communication shall be effective upon receipt
     by or tender for delivery to the intended recipient thereof.

17.0 NO WAIVERS.  Failure of either Landlord or Tenant to complain of any
     act or omission on the part of the other, no matter how long the same may
     continue, shall not be deemed to be a waiver by such non-complaining party
     of any of its rights hereunder. No waiver by either Landlord or Tenant at
     any time, expressed or implied, of any breach of any provision of this
     Sublease shall be deemed a waiver of a breach of any other provision of
     this Sublease or a consent to any subsequent breach of the same or any
     other provision.  No acceptance by Landlord of any partial payment shall
     constitute an accord or satisfaction but shall only be deemed a partial
     payment on account; nor shall any endorsement or statement on any check or
     any letter accompanying any check or payment be deemed an accord and
     satisfaction, and Landlord may accept such check or payment without
     prejudice to Landlord's right to recover the balance of such installment
     or pursue any other remedy available to Landlord in this Sublease or at
     law or in equity.

          


                                      64

<PAGE>   17


18.0 LANDLORD'S OBLIGATIONS.

     18.1 GENERALLY.  Landlord shall:

          (a)  save Tenant harmless and indemnified from any
               loss, cost and expense (including, without limitation,
               reasonable attorney's fees) arising out of or relating to a
               claim of injury to any person or damage to any property while on
               the Premises or the Parking Area to the extent occasioned by any
               omission, neglect or default of Landlord or any officer, agent,
               employee, servant, contractor or invitee of Landlord.

          (b)  indemnify, defend, and hold harmless Tenant from
               and against any claim, cost, expense, liability, obligation or
               damage, including, without limitation, reasonable attorneys'
               fees and the cost of litigation, arising from or relating to the
               unlawful release or presence (whether now existing or hereafter
               arising) of Hazardous Materials in the Premises, to the extent
               occasioned by any negligent or wrongful act or omission of
               Landlord or any officer, agent, employee, servant, contractor or
               invitee of Landlord;
     
          (c)  not knowingly permit any officer, agent,
               employee, servant, contractor or visitor of Landlord to violate
               any covenant or obligation of Landlord hereunder; and
               
          (d)  to pay Tenant's reasonable expenses, including
               reasonable attorneys' fees, incurred in enforcing any
               obligations of Landlord under this Sublease.
               
     18.2 OVERLANDLORD'S MAINTENANCE.  Pursuant and subject to the
          terms and conditions of the Main Lease, it is the sole responsibility
          of Overlandlord to maintain: (i) the structural columns and beams of
          the Building, (ii) the exterior skin of the Building, and (iii) the
          Parking Area in good order, repair and condition, except as otherwise
          set forth in the Main Lease. Landlord agrees to use all reasonable
          efforts to enforce the obligations of Overlandlord under the Main
          Lease, but Tenant expressly agrees that Landlord shall have no
          obligation or liability for any such maintenance over and above
          Landlord's obligation to use such reasonable efforts, and Tenant
          shall reimburse Landlord on demand any costs or expenses incurred in
          connection with such efforts.

     18.3 SERVICES.  Pursuant and subject to the terms and conditions
          of the Main Lease, it is the sole responsibility of Overlandlord to
          provide to the Premises during the Lease Term (collectively,
          "Overlandlord's Services") shall be: (i) maintenance of the Parking
          Area (including snowplowing and sweeping), (ii) lighting of the
          Parking Area (including maintaining such lighting system), and (iii)
          such other services (if any) as Overlandlord may reasonably determine
          from time to time are necessary for the maintenance and operation of
          the Premises and which either are not provided by Landlord or Tenant
          or cannot, as a matter of law, be provided to the Premises in the
          name of Landlord or Tenant. Landlord is obligated under the Main
          Lease to reimburse Overlandlord for a portion of the cost of
          providing such services. Tenant agrees to reimburse Landlord an
          amount equal to 82.5% of all amounts paid by Landlord to Overlandlord
          in connection with services provided by Overlandlord under the Main
          Lease. Within a reasonable time after the end of each of
          Overlandlord's fiscal years (or portion thereof) occurring during the
          Lease Term, Landlord shall deliver to Tenant (i) a statement of the
          cost of such 
          


                                      65

<PAGE>   18

          Services for the fiscal year just ended (the  "Statement"), and (ii)
          an itemization of the amount of Tenant's share of the cost of 
          Landlord's Services for such fiscal year. Tenant shall pay to
          Landlord, as Additional Rent, within twenty (20) days of its receipt
          of the Statement, the amount shown thereon as Tenant's share of the
          cost of such Services for such fiscal year.
          
          Neither Overlandlord nor Landlord shall ever be held liable
          to anyone for the cessation of any of such Services due to any
          accident, to the making of repairs, alterations or improvements, or
          to the occurrence of an event of "Force Majeure" (as hereinafter
          defined).  Landlord shall have no obligation to provide any services
          of whatever nature to the Premises. Landlord agrees to use all
          reasonable efforts to enforce the obligations of Overlandlord under
          the Main Lease to provide such Services, but Tenant expressly agrees
          that Landlord shall have no obligation or liability for the same over
          and above Landlord's obligation to use such reasonable efforts, and
          Tenant shall reimburse Landlord on demand any costs or expenses
          incurred in connection with such efforts.

19.0 SUBORDINATION OF SUBLEASE; CONSENTS.

     19.1 INTENTIONALLY OMITTED

     19.2 LEASE SUBORDINATE.  This Sublease is and shall be subject
          and subordinate to the Main Lease, and to each and every term and
          provision thereof, and to any ground lease or mortgage now or
          hereafter affecting the Land, the Building or the Premises. In the
          event of any termination of the Main Lease, for whatever reason,
          including without limitation operation of law or agreement of the
          parties, prior to the expiration or earlier termination of the Lease
          Term, this Sublease shall immediately cease and terminate, without
          further obligation or liability of Landlord or Tenant (except as to
          those liabilities that expressly survive the expiration hereof).
          Notwithstanding the foregoing, Landlord shall obtain the written
          agreement of Overlandlord whereby if, as a result of a default by
          Landlord under the Main Lease, Overlandlord shall succeed to the
          interests of Landlord hereunder, then so long as no Event of Default
          on the part of Tenant exists hereunder and Tenant continues to
          perform it obligations hereunder, Tenant's right to possession of the
          Premises and other rights under this Sublease shall not be disturbed
          by Overlandlord, and Tenant shall attorn to and accept Overlandlord
          as the Landlord hereunder.

     19.3 CONSENTS.  Where any such consent is required or requested,
          Landlord may withhold the same for any reason, unless this Sublease
          expressly states that such consent shall not be unreasonably
          withheld. Wherever under this Sublease, Landlord's consent is
          required or is otherwise requested, and the consent of Overlandlord
          is also required, Landlord shall under no circumstances have any
          liability for failure to give such consent unless and until
          Overlandlord shall have given its consent. Tenant shall reimburse
          Landlord for any cost or expense incurred by Landlord in evaluating a
          request for consent or approval, or for preparation and negotiation
          of any necessary documentation in connection therewith.

20.0 NOTICE OF LEASE; ESTOPPEL CERTIFICATES.  Landlord and Tenant agree
     that this Sublease shall not be recorded. From time to time during the
     Lease Term, and without charge, either party shall, within ten (10)
     business days of request by the other, certify by written instrument duly
     executed and acknowledged, to the requesting party or to any person
     reasonably specified by the requesting party, regarding (a) the existence
     of any amendments or supplements to this Sublease; 
          


                                      66

<PAGE>   19

     (b) the validity and force and effect of this Sublease; (c) the existence
     of any known default or Event of Default; (d) the existence of any
     offsets, counterclaims or defenses; (e) the amount of Rent due and payable
     and the date to which Rent has been paid; and (f) any other matter
     reasonably requested.

21.0 HOLDING OVER.  If Tenant occupies the Premises after the day on which
     the Lease Term expires (or the effective date of any earlier termination
     as herein provided) without having entered into a new lease thereof with
     Landlord, Tenant shall be a tenant-at-sufferance only, subject to all of
     the terms and provisions of this Sublease at (x) two (2) times the
     then-effective Basic Rent stated in Section 3.0 hereof with respect to the
     Initial Term and the First Extended Term; and (y) three (3) times the
     then-effective Basic Rent stated in Section 3.0 hereof with respect to the
     Second Extended Term, provided that, if Tenant shall hold over for more
     than six (6) months after the expiration of either the Initial Term or the
     First Extended Term, then Tenant shall thereafter pay Basic Rent at the
     rate described in clause (y). Such a holding over, even if with the
     consent of Landlord, shall not constitute an extension or renewal of this
     Sublease. For purposes of this Section, the failure of Tenant to complete
     by the last day of the Lease Term or the effective date of any earlier
     termination as herein provided the "close-out" procedures required by the
     Nuclear Regulatory Commission or any other federal, state or local
     governmental agency having jurisdiction over the use of radioactive
     materials within the Premises shall constitute a holding over and subject
     Tenant to the provisions of this Section.
     
22.0 FORCE MAJEURE.  Neither Landlord nor Tenant shall be deemed to be in
     default hereunder (and the time for performance of any of their respective
     obligations hereunder other than the payment of money shall be postponed)
     for so long as the performance of such obligation is prevented by strike,
     lock-out, act of God, absence of materials or any other matter not
     reasonably within the control of the party which must perform the
     obligation (collectively, "Force Majeure").


23.0 SIGNS.  Tenant shall have the right to install one or more signs on
     the Building, identifying its name and business, provided that (i) Tenant
     shall obtain the prior written approval of Landlord and Overlandlord as to
     the location, size, shape and appearance of such signs, and as to the
     plans and specifications relating to such installation; (ii) Tenant shall
     install such signs at its sole cost; (iii) Tenant shall, at its sole cost,
     obtain all licenses, permits and other governmental consents and approvals
     required by applicable Legal Requirements to install such signs; (iv)
     Tenant shall cause such installation to be done in a good and workmanlike
     manner and in accordance with all applicable Legal Requirements, the
     provisions of applicable insurance policies, and the requirements of all
     existing restrictions, easements and encumbrances of record affecting the
     Land; (v) Tenant shall, at its sole cost, maintain such signs in good
     operating condition and in accordance with all applicable Legal
     Requirements, the provisions of applicable insurance policies, and the
     requirements of all existing restrictions, easements and encumbrances of
     record affecting the Land; and (vi) Tenant shall, at its sole cost, remove
     such signs on or prior to the date on which the Lease Term expires or this
     Sublease is terminated and restore the Premises to the condition in which
     it was prior to the installation of such signs.

     All work done by or on behalf of Tenant pursuant to this Section 23.0
     shall be subject to the requirements set forth in Section 11.0(f) above.
     Landlord or Overlandlord may inspect such work at any time or times.
     Tenant shall indemnify, defend and hold harmless Landlord and Overlandlord
     from and against any and all liability, damage, penalties or judgments and
     from and against any claims, actions, proceedings and expenses and costs
     in connection therewith, 

          


                                      67

<PAGE>   20

     including reasonable attorneys' fees, resulting from any work performed by
     or on behalf of Tenant pursuant to this Section 23.0.  Such signs shall
     be at Tenant's sole risk, and neither Landlord nor Overlandlord shall have
     any responsibility to maintain any insurance on them or otherwise be
     responsible for any damage or destruction thereto.
     
24.0 CONDITION AND IMPROVEMENT.  Tenant agrees that it is accepting the
     Premises in their current AS IS condition, without further representation
     by Landlord. Notwithstanding the foregoing, Landlord agrees that it shall,
     promptly upon full approval and execution hereof by all parties, undertake
     to complete the work described on Exhibit D hereto, according to plans and
     specifications to be prepared by Landlord and approved by Tenant and, if
     required, by Overlandlord. Upon such approval, such work shall be
     performed by Landlord at the sole cost and expense of Tenant, and Tenant
     shall reimburse Landlord for the actual costs incurred in connection with
     the performance of such work, such amount to be paid as Additional Rent
     within 15 days after completion of such work and receipt by Tenant of an
     invoice reflecting such costs.
     
25.0 ENTIRE AGREEMENT.  No oral statement or prior written matter shall
     have any force or effect.  This Agreement shall not be modified or
     canceled except by writing subscribed to by all parties.
     
26.0 APPLICABLE LAW, SEVERABILITY AND CONSTRUCTION.  This Sublease shall
     be governed by and construed in accordance with the laws of Massachusetts
     and, if any provisions of this Sublease shall to any extent be invalid,
     the remainder of this Sublease, and the application of such provisions in
     other circumstances, shall not be affected thereby.  The titles of the
     several Sections contained herein are for convenience only and shall not
     be considered in construing this Sublease.  Whenever the singular is used
     and when required by the context it shall include the plural, and the
     neuter gender shall include the masculine and feminine.  The Exhibits
     attached to this Sublease are incorporated into this Sublease by
     reference.  This Sublease may be executed in several counterparts, each of
     which shall be an original, but all of which shall constitute one and the
     same instrument.  The term "Landlord" whenever used herein, shall mean
     only the owner at the time of sublessor's interest herein, and no covenant
     or agreement of Landlord, express or implied, shall be binding upon any
     person except for defaults occurring during such person's period of
     ownership nor binding individually upon any officer, director, employee,
     fiduciary, shareholder or any beneficiary under any trust.  If Tenant is
     several persons or a partnership, Tenant's obligations are joint or
     partnership and also several.  Unless repugnant to the context, "Landlord"
     and "Tenant" mean the person or persons, natural or corporate, named above
     as Landlord and as Tenant respectively, and their respective heirs,
     executors, administrators, successors and assigns.
     
27.0 SUCCESSORS AND ASSIGNS.  The terms, covenants and conditions of this
     Sublease shall be binding upon and inure to the benefit of Landlord and
     Tenant and their respective successors and permitted assigns.
     
28.0 INTENTIONALLY OMITTED.
     
29.0 AUTHORITY.  Contemporaneously with the signing of this Sublease,
     Tenant shall furnish to Landlord a certified copy of the resolution of the
     Board of Directors of Tenant authorizing Tenant to enter into this
     Sublease.
     
          


                                      68

<PAGE>   21
     
     
     WITNESS the execution hereof in multiple counterparts under seal the
     day and year first above written.


     Landlord:                     IMMUNOGEN, INC.

                                   By:  /S/FRANK J. POCHER
                                        ------------------
                                   Name:  Frank J. Pocher
                                   Title:  Vice President
                                   Hereunto duly authorized
                                   Date:  August 31, 1995

     Tenant:                       ASTRA RESEARCH CENTER BOSTON, INC.

                                   By:  /S/HANS G. NILSSON
                                        ------------------
                                   Name:  Hans G. Nilsson
                                   Title: President
                                   Hereunto duly authorized
                                   Date:  August 31, 1995










          


                                      69



<PAGE>   1
                                                                Exhibit 10.24

                     EQUIPMENT USE AND SERVICES AGREEMENT

Dated:    August 31, 1995

                            PRELIMINARY  STATEMENT
                                       
     By a Sublease (the "Sublease") of even date herewith, IMMUNOGEN, INC.
("Landlord") has sublet unto ASTRA RESEARCH CENTER BOSTON, INC. a Massachusetts
corporation ("Tenant"), certain premises, being a portion of the building known
as and numbered 128 Sidney Street, Cambridge, Massachusetts (the "Building"),
which portion contains approximately 30,778 rentable square feet, more
particularly described in the Sublease (such portion of the Building being
sometimes hereinafter referred to as the "Premises"). In connection with the
Sublease, Tenant has requested that Landlord lease to Tenant certain equipment,
improvements and fixtures (individually and collectively, the "Equipment"),
more particularly described in this Agreement, currently owned by Landlord and
located in the Premises, for use by Tenant in connection with Tenant's use and
occupancy of the Premises. Terms not defined in this Agreement shall have the
meanings given them in the Sublease.

1.0  PARTIES AND PREMISES.  Landlord hereby leases unto Tenant the Equipment,
     which is more particularly listed and described on Exhibit A hereto.

2.0  TERM; COMMENCEMENT DATE;
 EXTENSION OPTION.

     2.1  TERM; COMMENCEMENT DATE.  The initial term of this
          Agreement (the "Initial Term") shall commence on September 1, 1995
          (the "Commencement Date") and shall expire on the same date as the
          expiration or earlier termination of the term of the Sublease (as
          such term may be extended in accordance with the terms and conditions
          thereof).

3.0  RENT; NET LEASE

     3.1  DEFINITIONS; PAYMENT OF RENT.  Tenant shall pay Landlord,
          without offset or deduction and without previous demand therefor, as
          items constituting rent (collectively, "Rent"):

          (a) Basic Rent at the following rates:
                
              (i)   $145,809.00 per annum for each Lease Year (as defined in 
                    the Sublease) of the Initial Term of the Sublease;

              (ii)  for each Lease Year during the First Extended Term of the 
                    Sublease, an amount equal to the product of (x) $145,809,
                    multiplied by (y) a fraction, the numerator of which is
                    the point at which the Index stood at the last day of the
                    Initial Term of the Sublease, and the denominator of which
                    is the point at which the Index stood at the date hereof.

              (iii) for each Lease Year during the Second Extended Term of the 
                    Sublease, an amount equal to the product of (x) the Rent
                    payable with respect to the First Extended Term, multiplied 
                    by (y) a fraction, the numerator of which is the point at
                    which the Index stood at the last day of the First Extended
                    Term, and the denominator of which is the point at which the
                    Index stood at the first day of the First Extended Term.


                                      71

<PAGE>   2
          (b) All other costs, charges, or expenses which Tenant in
          this Agreement agrees to pay, or which Landlord pays or incurs as the
          result of a default by Tenant hereunder, including any penalty or
          interest which may be added for nonpayment or late payment thereof as
          provided in this Agreement (collectively, "Additional Rent").

          (c) Rent shall be due and payable in equal monthly
          installments, in advance, as, when and where Rent is payable under
          the terms of the Sublease. Rent for the month of September, 1995
          shall be paid on execution hereof.

3.4  NET LEASE.  It is the intention of the Landlord and the Tenant that
     this is a "net" lease and that the Rent herein specified shall be paid to
     the Landlord in each month during the term of the Sublease, and that all
     costs, expenses, and obligations of every kind relating to the Equipment,
     whether usual or unusual, ordinary or extraordinary, foreseen or
     unforeseen, which may arise or become due during the term of the Sublease,
     shall be paid by Tenant except as otherwise specifically provided herein.

4.0  PERMITTED USE.  The Equipment shall be used by Tenant only on the
     Premises and in connection with Permitted Uses set forth in the Sublease,
     and shall not be removed from the Premises (other than temporary removal
     to facilitate maintenance or repair).
     
     5.0  TAXES.
     
     5.1  TAXES.  Tenant shall pay as Additional Rent all excise or
          other personal property taxes, special or general assessments, rates
          and charges and other impositions and charges imposed on Landlord or
          Overlandlord in respect of the Equipment, as well as any tax based on
          a percentage fraction or capitalized value of the Rent (whether in
          lieu of or in addition to the taxes hereinbefore described)
          (collectively, "Taxes"). Landlord shall use its best efforts to send
          copies of all bills for Taxes to Tenant within ten (10) days of
          Landlord's receipt thereof.  Tenant shall pay to Landlord, as
          Additional Rent all Taxes so assessed, within ten (10) days of
          Tenant's receipt of such copy of the bill. Provided that Tenant pays
          such Taxes to Landlord within the time provided in this Section 5.2,
          Landlord shall pay the Taxes to the taxing authority (or to
          Overlandlord, if required) in a timely manner. Tenant's obligations
          under this Section 5 shall be pro-rated for partial tax years at the
          beginning or end of the term of the Sublease.
     
6.0  INTENTIONALLY OMITTED.

7.0  INSURANCE

     7.1  PUBLIC LIABILITY INSURANCE.  In addition to insurance
          coverage to be obtained by Tenant pursuant to the Sublease, Tenant
          shall take out, at its sole cost and expense, and maintain in force
          throughout the term of the Sublease, property damage insurance
          (including without limitation so-called "contents and improvements"
          coverage), covering the Equipment against all risks, and insuring the
          full replacement value of the Equipment. Landlord shall be named as
          an additional insured under each such policy, as its interest may
          appear. Alternatively, Landlord may elect to take out and maintain
          such insurance in connection with the property damage insurance
          Landlord is obligated to carry under the Main Lease, in which case
          Tenant shall reimburse Landlord for all premiums related to such
          Equipment coverage.


                                      72

<PAGE>   3
          All insurance policies maintained pursuant to this Section
          7.2 shall include insurance, if available, against payment of rents
          in an amount sufficient to pay all Rent which would otherwise be
          required to be paid under this Agreement during the period of and
          repair or replacement.

     7.3  CERTIFICATE OF INSURANCE.  All insurance required to be
          maintained by Tenant hereunder: shall be placed with insurers
          reasonably satisfactory to Landlord and authorized to do business in
          Massachusetts; shall provide that it may not be canceled without at
          least thirty (30) days prior written notice to each additional
          insured or certificate holder named therein; and shall provide that
          it may not be amended without at least fifteen (15) days prior
          written notice to each such person.  Tenant shall furnish to Landlord
          certificates of insurance for all insurance required to be maintained
          by Tenant under this Agreement, together with evidence satisfactory
          to Landlord of the payment of all premiums for such policies. Tenant,
          at Landlord's request, shall also deliver such certificates and
          evidence of payment to the holder of any mortgage affecting the
          Premises or any portion thereof.

     7.4  WAIVER OF SUBROGATION.  To the extent to which a waiver of
          subrogation clause is available, Landlord and Tenant shall obtain a
          provision in all insurance policies carried by such party covering
          the Premises, including but not limited to contents, fire and
          casualty insurance, expressly waiving any right on the part of the
          insurer against the other party.  If extra cost is chargeable for
          such provision, then Tenant shall pay such extra charge.
          
     7.5  WAIVER OF RIGHTS.  All claims, causes of action and rights
          of recovery for any damage to or destruction of persons, property or
          business which shall occur on or about the Premises which result from
          any of the perils insured under any and all policies of insurance
          maintained by Landlord or Tenant, are waived by each party as against
          the other party, and the officers, directors, employees, contractors,
          servants and agents thereof, regardless of cause, including the
          negligence of the other party and its respective officers, directors,
          employees, contractors, servants and agents, but only to the extent
          of recovery, if any, under such policy or policies of insurance;
          provided, however, that this waiver shall be null and void to the
          extent that any such insurance shall be invalidated by reason of this
          waiver.

8.0  ASSIGNMENT AND SUBLETTING.  Tenant shall not mortgage, pledge,
     hypothecate, or assign this Agreement or sublease the Equipment or any
     portion thereof (which term shall be deemed to include any arrangement
     pursuant to which a third party is permitted by Tenant to use the
     Equipment for any purpose).

9.0  INTENTIONALLY OMITTED.

10.0 LATE PAYMENT OF RENT.  Tenant agrees that in the event that any
     payment of Basic Rent or Additional Rent shall remain unpaid at the close
     of business on (x) with respect to Basic Rent, the seventh (7th) business
     day after the same is due and payable hereunder, and (y) with respect to
     Additional Rent, the seventh (7th) business day after receipt of
     Landlord's invoice therefor, there shall become due to Landlord from
     Tenant, as Additional Rent and as compensation for Landlord's extra
     administrative costs in investigating the circumstances of late Rent, a
     late charge of five percent (5%) of the amount overdue.  The assessment or
     collection of such a 


                                      73

<PAGE>   4

     charge shall not be deemed to be a waiver by Landlord
     of any default by Tenant arising out of such failure to pay Rent when due.
     
11.0 TENANT'S COVENANTS.  Tenant acknowledges that the Equipment is in
     good and satisfactory order, repair and condition, and covenants, at its
     sole cost and expense, during the term of the Sublease and such further
     time as Tenant uses the Equipment or holds any part of the Premises:

     (a)  to pay when due the Basic Rent and all Additional Rent, and
          all charges for repair, maintenance and replacements of or to the
          Equipment pursuant to agreements between Tenant and the appropriate
          provider of such services;

     (b)  to keep the Equipment in as good order, repair and
          condition as the same are in as of the date of this Agreement,
          excepting only damage by fire or other casualty or taking which
          Tenant is not otherwise required by the terms of this Agreement to
          repair or restore, but specifically including wear and tear. The
          Equipment shall be used, maintained, repaired and replaced in
          conformance with recommended schedules, guidelines and manufacturers'
          manuals. In connection therewith and without limitation thereof, with
          respect to the Equipment described on Exhibit A-1 hereto, Tenant
          shall maintain in full force and effect throughout the term of the
          Sublease one or more service and maintenance agreements or contracts
          with factory-qualified and certified contractors, and shall perform
          all requirements of any warranties or guaranties, so as to keep the
          same in effect at all times. Copies of all such agreements and
          contracts shall be delivered to Landlord from time to time. Landlord
          hereby assigns to Tenant (and will separately assign, as required)
          all of Landlord's right to enforce or recover under any such
          warranties or guaranties, for the term of the Sublease;
          
     (c)  not to injure, overload or deface the Equipment, nor
          knowingly to suffer or commit any waste thereof, nor to use or
          operate any of the Equipment except in full compliance with all laws,
          ordinances, codes, rules and regulations, and the provisions of any
          license, permit or other governmental consent or approval required
          for or applicable to the Equipment at any time during the term of the
          Sublease;
          
     (d)  to obtain and maintain in full force and effect all
          licenses, permits and governmental consents and approvals required by
          any Legal Requirement for the operation of the Equipment, and to
          procure (and maintain in full force and effect) all licenses, permits
          and other governmental consents and approvals required by any Legal
          Requirement or by the provisions of any applicable insurance policy
          because of the use made of the Equipment by Tenant;
          
     (e)  not to make any alterations, renovations, improvements
          and/or additions to the Equipment (collectively, "Alterations"),
          without on each occasion obtaining prior written consent of Landlord,
          which consent may be withheld by Landlord in its reasonable
          discretion. Prior to commencing any Alterations, Tenant shall comply
          with all applicable requirements of the Sublease in respect of any
          Alterations. Tenant shall pay promptly when due the entire cost of
          such work.  Tenant shall not cause or permit any liens for labor or
          materials performed or furnished in connection therewith to attach to
          the Equipment, and shall discharge or bond any such liens which may
          be filed within ten (10) days after the filing thereof. All such work
          shall be performed in a good and workmanlike manner and in compliance
          with all Legal Requirements and the provisions of 




                                      74

<PAGE>   5
        
          all applicable insurance policies.  Promptly after the completion of
          any Alterations, Tenant shall provide an as-built plan (or, where
          appropriate in light of the nature or scope of the Alterations, an    
          as-built sketch) thereof to Landlord.  Tenant shall indemnify and hold
          Landlord and Overlandlord harmless from and against any and all suits,
          demands, causes of action, claims, losses, debts, liabilities,
          damages, penalties or judgments, including, without limitation,
          reasonable attorneys' fees, arising from injury to any person or
          damage to any property occasioned by or growing out of such work
          performed prior to the last day of the term of the Sublease, which
          indemnity shall survive the expiration or termination of this
          Agreement;
          
     (f)  to save Landlord and Overlandlord harmless and indemnified
          from any loss, cost and expense (including, without limitation,
          reasonable attorney's fees) arising out of or relating to a claim of
          injury to any person or damage to any property arising out of the
          presence, use, maintenance, repair or operation of the Equipment, if
          not due to the negligence or willful misconduct of Landlord,
          Overlandlord or their respective officers, agents, employees,
          servants or contractors, or the breach of Landlord's obligations
          under this Agreement. The provisions of this clause (f) shall survive
          the expiration or termination of this Agreement with respect to any
          claim arising prior to the last day of the term of the Sublease;
          
     (g)  to permit Landlord and its agents to examine the Equipment
          at reasonable times (provided 24 hours notice is given to Tenant,
          except in case of emergency), and if Landlord shall so elect (without
          hereby imposing any obligation on Landlord to do so), to permit
          Landlord to make any repairs, replacements or additions Landlord may
          deem necessary;
          
     (h)  by 5:00 p.m., local time, on the last day of the term of
          the Sublease (or the effective date of any earlier termination of
          this Agreement as herein provided), to peaceably to yield up the
          Equipment clean and in good order, repair and condition (excepting
          only damage by fire or other casualty or taking which Tenant is not
          otherwise required by the terms of this Agreement to repair or
          restore); and to deliver the same to Landlord.  Tenant hereby
          acknowledges that any failure or delay on Tenant's part in
          surrendering the Equipment as above provided may subject Landlord to
          liability to Overlandlord;
     (i)  to pay Landlord's reasonable expenses (including without
          limitation any costs or expenses that Landlord may have to pay to
          Overlandlord), including reasonable attorneys' fees, incurred in
          enforcing any obligations of Tenant under this Agreement;

     (j)  not knowingly to permit any officer, agent, employee,
          servant, contractor or visitor of Tenant to violate any covenant or
          obligation of Tenant hereunder.

12.0 INTENTIONALLY OMITTED.

13.0 EMINENT DOMAIN AND CASUALTY. In the event that the Sublease shall be
     terminated as a result of any taking, fire or other casualty or event
     described therein, this Agreement shall similarly terminate immediately
     prior to the termination of the Sublease, and Landlord shall have no
     liability or obligation to Tenant as a result of such termination.

     13.1 SUBSTANTIAL TAKING.  In the event that any of the Equipment
          is taken due to any exercise of the right of eminent domain or other


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<PAGE>   6
          lawful power in pursuance of any public or other authority during the
          term of the Sublease, then this Agreement shall terminate as to the
          Equipment so taken immediately prior to the possession thereof by the
          taking authority.
          
     13.2 PARTIAL TAKING.  In the event that a taking of some or all
          of the Equipment occurs, and in Tenant's reasonable opinion, such
          taking will render it impracticable for Tenant to continue Permitted
          Uses in the Premises, and if Landlord is unable to replace the
          Equipment so taken within a reasonable period of time, then either
          Landlord or Tenant shall have the right to terminate this Agreement
          by giving the other party notice of its desire to do so, within 30
          days after notice of such taking, such termination to be effective on
          the day preceding the date possession is taken by the taking
          authority.
          
     13.3 AWARDS. Landlord reserves and excepts all rights to damage
          to the Equipment and the leasehold hereby created, now accrued or
          hereafter accruing by reason of any exercise of eminent domain, or by
          reason of anything done in pursuance of any public or other
          authority, and by way of confirmation, Tenant grants to Landlord any
          and all of Tenant's rights to such damages and covenants to execute
          and deliver such further instruments of assignment thereof as
          Landlord may from time to time request. To the extent that a taking
          of Equipment occurs and Tenant elects not to terminate this
          Agreement, and replaces or repairs such Equipment, then Landlord
          shall turn over to Tenant such portion of the proceeds actually
          received by Landlord as are required therefor.
          
     13.4 SUBSTANTIAL CASUALTY.  If the Equipment is damaged by fire
          or other casualty, Tenant shall promptly notify Landlord thereof. If
          the Sublease is terminated due to any fire or casualty, then this
          Agreement shall terminate immediately prior to the termination of the
          Sublease. In the event that this Agreement is terminated pursuant to
          this Section 13.4: (i) Rent shall be abated from and after the date
          of such damage to the date of such termination of this Agreement, and
          no further Rent shall accrue or be payable after the date of such
          termination; and (ii) Tenant shall turn over and assign to Landlord
          all insurance proceeds (and rights to receive the same) relating to
          the Equipment.
          
     13.5 REPAIR AND RESTORATION. In the event of a taking which does
          not result in the termination of this Agreement pursuant to Section
          13.1 above, or a casualty which does not result in the termination of
          this Agreement pursuant to Section 13.4 above, the Equipment shall be
          repaired, replaced and restored, as necessary, by Tenant to its prior
          condition and utility, and Tenant shall have the use of any insurance
          or condemnation proceeds available therefor. Neither Overlandlord nor
          Landlord shall be liable for any inconvenience or annoyance to Tenant
          or injury to the business of Tenant resulting in any way from such
          taking or damage or the repair thereof.
          
     13.6 CASUALTY DURING LAST 6 MONTHS.  Notwithstanding anything to
          the contrary contained in this Agreement, in the event that a
          material portion of the Equipment is damaged by a fire or other
          casualty occurring during the last six (6) months of the term of the
          Sublease, either party may terminate this Agreement by giving written
          notice to the other within twenty (20) days of the occurrence of such
          damage. If this Agreement is so terminated, or if this Agreement is
          terminated as a result of any termination of the Sublease pursuant to
          Article 13 thereof, Tenant shall turn over and assign to Landlord all
          insurance proceeds (and rights to receive the same) relating to the
          Equipment.



                                      76

<PAGE>   7
14.0 DEFAULTS; EVENTS OF DEFAULT; REMEDIES.

     14.1 DEFAULTS; EVENTS OF DEFAULT.  The following shall, if any
          requirement for notice or lapse of time or both has not been met,
          constitute defaults hereunder, and, if such requirements have been
          met, constitute "Events of Default" hereunder:

               (a)  The failure of Tenant to perform or observe any of Tenant's 
                    covenants or agreements hereunder concerning the payment of
                    money for a period of five (5) days after written notice
                    thereof, provided, however, that Tenant shall not be
                    entitled to such notice if Landlord has given notice to
                    Tenant of two or more previous such failures within a
                    twelve-month period, in which event such failure shall
                    constitute an Event of Default hereunder upon the expiration
                    of five (5) days after such payment was due;
                    
               (b)  The failure of Tenant to maintain any insurance required 
                    hereunder in full force and effect;
                    
               (c)  The failure of Tenant to perform or observe any of Tenant's
                    other covenants or agreements hereunder for a period of
                    twenty (20) days after written notice thereof (provided
                    that, in the case of defaults not reasonably curable in
                    twenty (20) days through the exercise of reasonable
                    diligence, such 20-day period shall be extended for so long
                    as Tenant commences cure within such period and thereafter
                    prosecutes such cure to completion continuously and with
                    reasonable diligence);
                    
               (d)  The occurrence of any Event of Default on the part of 
                    Tenant under the Sublease;
                    
               (e)  if the leasehold hereby created shall be taken on execution,
                    or by other process of law, and such taking is not vacated
                    by a final order of a court of competent jurisdiction
                    within sixty (60) days thereafter.

     14.2 TERMINATION; RIGHTS AND REMEDIES.  If an Event of Default
          shall occur, Landlord shall have any or all of the rights and
          remedies described in the Sublease, and such rights and remedies
          shall apply equally to the Equipment and the Premises.
          
15.0 INTENTIONALLY OMITTED.

16.0 NOTICES.  Any notices given hereunder shall be given in accordance with
     the Sublease.

17.0 NO WAIVERS.  Failure of either Landlord or Tenant to complain of any
     act or omission on the part of the other, no matter how long the same may
     continue, shall not be deemed to be a waiver by such non-complaining party
     of any of its rights hereunder. No waiver by either Landlord or Tenant at
     any time, expressed or implied, of any breach of any provision of this
     Agreement shall be deemed a waiver of a breach of any other provision of
     this Agreement or a consent to any subsequent breach of the same or any
     other provision.  No acceptance by Landlord of any partial payment shall
     constitute an accord or satisfaction but shall only be deemed a partial
     payment on account; nor shall any endorsement or statement on any check or
     any letter accompanying any 


                                      77

<PAGE>   8

     check or payment be deemed an accord and satisfaction, and Landlord may
     accept such check or payment without prejudice to Landlord's right to
     recover the balance of such installment or pursue any other remedy
     available to Landlord in this Agreement or at law or in equity.

18.0 LANDLORD'S OBLIGATIONS.

     18.1 GENERALLY.  Landlord shall:

          (a)  save Tenant harmless and indemnified from any
               loss, cost and expense (including, without limitation,
               reasonable attorney's fees) arising out of or relating to a
               claim of injury to any person or damage to any property, to the
               extent occasioned by any omission, neglect or default of
               Landlord or any officer, agent, employee, servant, contractor or
               invitee of Landlord, in respect of the Equipment;
               
          (b)  not knowingly permit any officer, agent, employee, servant, 
               contractor or visitor of Landlord to violate any covenant or 
               obligation of Landlord hereunder; and
               
          (c)  to pay Tenant's reasonable expenses, including reasonable 
               attorneys' fees, incurred in enforcing any obligations of 
               Landlord under this Agreement.

19.0 CONSENTS.  Where any such consent is required or requested, Landlord
     may withhold the same for any reason, unless this Agreement expressly
     states that such consent shall not be unreasonably withheld. Wherever
     under this Agreement, Landlord's consent is required or is otherwise
     requested, and the consent of Overlandlord is also required, Landlord
     shall under no circumstances have any liability for failure to give such
     consent unless and until Overlandlord shall have given its consent. Tenant
     shall reimburse Landlord for any cost or expense incurred by Landlord in
     evaluating a request for consent or approval, or for preparation and
     negotiation of any necessary documentation in connection therewith.

20.0 ESTOPPEL CERTIFICATES. From time to time during the term of the
     Sublease, and without charge, either party shall, within ten (10) business
     days of request by the other, certify by written instrument duly executed
     and acknowledged, to the requesting party or to any person reasonably
     specified by the requesting party, regarding (a) the existence of any
     amendments or supplements to this Agreement; (b) the validity and force
     and effect of this Agreement; (c) the existence of any known default or
     Event of Default; (d) the existence of any offsets, counterclaims or
     defenses; (e) the amount of Rent due and payable and the date to which
     Rent has been paid; and (f) any other matter reasonably requested.

21.0 HOLDING OVER.  If Tenant retains use of any or all of the Equipment
     after the day on which the term of the Sublease expires (or the effective
     date of any earlier termination as herein provided) without having entered
     into a new lease thereof with Landlord, Tenant shall be a
     tenant-at-sufferance only, subject to all of the terms and provisions of
     this Agreement at (x) two (2) times the then-effective Basic Rent stated
     in Section 3.0 hereof with respect to the Initial Term and the First
     Extended Term; and (y) three (3) times the then-effective Basic Rent
     stated in Section 3.0 hereof with respect to the Second Extended Term,
     provided that, if Tenant shall hold over for more than six (6) months
     after the expiration of either the Initial Term or the First Extended
     Term, then Tenant shall thereafter pay Basic Rent at the rate described in
     clause (y). Such a holding over, even if with the consent of Landlord,
     shall not constitute an extension or 


                                      78

<PAGE>   9

     renewal of this Agreement. For purposes of this Section, the failure of
     Tenant to complete by the last day of the term of the Sublease or the
     effective date of any earlier termination as herein provided the
     "close-out" procedures required by the Nuclear Regulatory Commission or
     any other federal, state or local governmental agency having jurisdiction
     over the use of radioactive materials within the Premises shall constitute
     a holding over and subject Tenant to the provisions of this Section.
     
22.0 FORCE MAJEURE.  Neither Landlord nor Tenant shall be deemed to be in
     default hereunder (and the time for performance of any of their respective
     obligations hereunder other than the payment of money shall be postponed)
     for so long as the performance of such obligation is prevented by strike,
     lock-out, act of God, absence of materials or any other matter not
     reasonably within the control of the party which must perform the
     obligation (collectively, "Force Majeure").
     
23.0 INTENTIONALLY OMITTED.

24.0 CONDITION.  Tenant agrees that it is accepting the Equipment in its
     current AS IS condition, without further representation by Landlord.

25.0 ENTIRE AGREEMENT.  No oral statement or prior written matter shall have
     any force or effect.  This Agreement shall not be modified or canceled
     except by writing subscribed to by all parties.

26.0 APPLICABLE LAW, SEVERABILITY AND CONSTRUCTION.  This Agreement shall
     be governed by and construed in accordance with the laws of Massachusetts
     and, if any provisions of this Agreement shall to any extent be invalid,
     the remainder of this Agreement, and the application of such provisions in
     other circumstances, shall not be affected thereby.  The titles of the
     several Sections contained herein are for convenience only and shall not
     be considered in construing this Agreement.  Whenever the singular is used
     and when required by the context it shall include the plural, and the
     neuter gender shall include the masculine and feminine.  The Exhibits
     attached to this Agreement are incorporated into this Agreement by
     reference.  This Agreement may be executed in several counterparts, each
     of which shall be an original, but all of which shall constitute one and
     the same instrument.  The term "Landlord" whenever used herein, shall mean
     only the owner at the time of sublessor's interest herein, and no covenant
     or agreement of Landlord, express or implied, shall be binding upon any
     person except for defaults occurring during such person's period of
     ownership nor binding individually upon any officer, director, employee,
     fiduciary, shareholder or any beneficiary under any trust.  If Tenant is
     several persons or a partnership, Tenant's obligations are joint or
     partnership and also several.  Unless repugnant to the context, "Landlord"
     and "Tenant" mean the person or persons, natural or corporate, named above
     as Landlord and as Tenant respectively, and their respective heirs,
     executors, administrators, successors and assigns.

27.0 SUCCESSORS AND ASSIGNS.  The terms, covenants and conditions of this
     Agreement shall be binding upon and inure to the benefit of Landlord and
     Tenant and their respective successors and permitted assigns.

28.0 INTENTIONALLY OMITTED.

29.0 AUTHORITY.  Contemporaneously with the signing of this Agreement,
     Tenant shall furnish to Landlord a certified copy of the resolution of the
     Board of Directors of Tenant authorizing Tenant to enter into this
     Agreement.



                                      79

<PAGE>   10

     WITNESS the execution hereof in multiple counterparts under seal the day
and year first above written.


     Landlord:                     IMMUNOGEN, INC.

                                   By:  /S/FRANK J. POCHER
                                        ------------------
                                   Name:  Frank J. Pocher
                                   Title:  Vice President
                                   Hereunto duly authorized
                                   Date:  August 31, 1995



     Tenant:                       ASTRA RESEARCH CENTER BOSTON, INC.

                                   By:  /S/HANS G. NILSSON
                                        ------------------
                                   Name:  Hans G. Nilsson
                                   Title:  President
                                   Hereunto duly authorized
                                   Date:  August 31, 1995
     EXHIBIT A
     [LIST OF EQUIPMENT]
     EXHIBIT A-1

[LIST OF EQUIPMENT REQUIRING SERVICE CONTRACTS]






                                      80

<PAGE>   11
                                                                Exhibit 10.25

                       CONSENT TO SUBLEASE AND AGREEMENT
                       ---------------------------------
                
     THIS CONSENT TO SUBLEASE AND AGREEMENT is made this 31st day of August,
1995, by and between MASSACHUSETTS INSTITUTE OF TECHNOLOGY, a Massachusetts
educational corporation with a principal place of business at 238 Main Street,
Suite 200, Cambridge, Massachusetts 02142 ("Lessor"), IMMUNOGEN, INC., a
Massachusetts corporation with an address of 148 Sidney Street, Cambridge,
Massachusetts 02139 ("Sublessor") and ASTRA RESEARCH CENTER BOSTON, INC., a
Massachusetts corporation with an address of 128 Sidney Street, Cambridge,
Massachusetts 02139 ("Sublessee").

     WHEREAS, Lessor, as lessor, and Sublessor, as lessee, entered into a
certain lease dated December 23, 1992 (the "Overlease") for the land and
buildings known as and numbered 128 Sidney Street, Cambridge, Middlesex County,
Massachusetts (the "Leased Premises"); and

     WHEREAS, Sublessor now desires to sublease a portion of the Leased
Premises to Sublessee upon the terms and conditions set forth in a sublease
dated August 31, 1995, a copy of which is attached hereto and incorporated
herein as Exhibit "A" (the "Sublease"); and

     WHEREAS, Lessor desires to consent to the Sublease solely upon the terms
and conditions hereinafter set forth and in consideration of the undertakings
of Sublessor and Sublessee as set forth herein;

     NOW, THEREFORE, in consideration of the mutual covenants contained
hereinafter, and for other good and valuable consideration, the receipt and
sufficiency of which is hereby acknowledged, it is hereby agreed by and between
the parties as follows:

     1.   Lessor hereby consents to the Sublease from Sublessor to Sublessee in
the form attached hereto and incorporated herein as Exhibit "A", subject to the
terms and conditions hereinafter set forth.

     2.   Notwithstanding the consent of Lessor to the Sublease, Sublessor
shall remain directly and primarily responsible for any and all obligations of
Sublessor under the terms and conditions of the Overlease, including, but not
limited to any obligation to pay rent or additional rent pursuant to the terms
and conditions of said Overlease.  Further, Lessor's consent to the Sublease
shall in no manner be deemed to release Sublessor from any liability of any
nature whatsoever, and said consent shall not serve to release Sublessor, in
any manner, from any obligation or responsibility pursuant to the Overlease,
whether heretofore or hereafter arising.

     3.   Sublessor and Sublessee hereby acknowledge and agree that the
Sublease and all of Sublessee's rights pursuant to the Sublease are and shall
at all times be subject and subordinate to all of the terms, conditions and
limitations set forth in the Overlease, and any and all amendments thereto now
existing or hereinafter entered into by Lessor and Sublessor; and, in the event
of any conflict or variance between the terms and conditions of the Overlease
and this Sublease, on the other, the terms and conditions of the Overlease and
this Consent shall be deemed to control in each and every event and
circumstance, unchanged and unaltered by the terms and conditions of the
Sublease and notwithstanding any term or provision of the Sublease.

     4.   Sublessor and Sublessee hereby further covenant and agree that upon
the termination of the Overlease, for any reason whatsoever, the Sublease and
all rights of Sublease thereunder shall cease 





                                      82

<PAGE>   12
and determine, and Sublessee shall surrender each and every portion of the
Leased Premises occupied by Sublessee pursuant to the Sublease to Lessor in
accordance with the terms and conditions of the Overlease; provided, however,
that:

     (a)  Provided Sublessee is not then in default under the Sublease beyond
all applicable periods of grace and cure thereunder, in the event of a
cancellation or surrender or termination of the Overlease prior to the
expiration of the term of the Sublease:

          (1)  the Sublease shall not be terminated and shall continue in full
force and effect and Sublessee's possession of the premises demised thereunder
shall not be disturbed by Lessor;

               (2)  the Sublease shall continue, in the event of a termination
     of the Overlease as aforesaid, as a lease between Lessor, as landlord, and
     Sublessee, as tenant, with the same force and effect as if Lessor and
     Sublessee had entered into the Sublease as of the date of the termination
     of the Overlease on the same terms, covenants and conditions as those
     contained in the Sublease, including, without limitation, for a term equal
     to the unexpired term of the Sublease; PROVIDED that Lessor shall in no
     event be (A) liable or responsible or subject to any offsets or defenses
     for any act or failure to act by Sublessor or any other prior holder of
     the landlord's interest under the Sublease; or (B) liable for the return
     of any security deposit which Sublessee paid to Sublessor or any other
     prior holder of the landlord's interest under the Sublease; or (C) subject
     to any offsets or defenses which Sublessee might have against Sublessor or
     any other prior holder of the landlord's interest under the Sublease; or
     (D) bound by any rent, additional rent or any other payments which
     Sublessee might have paid for more than the current month to Sublessor or
     any other prior holder of the landlord's interest under the Sublease; or
     (E) bound by any amendment or modification of the Sublease made without
     Lessor's prior written consent; or (F) bound by any consent by Sublessor
     or Sublease to any assignment or sublease of the tenant's interest in the
     Sublease; or (G) liable for the payment of any sum(s) due from Sublessor
     or any other prior holder of the landlord's interest under the Sublease to
     Sublessee.  Notwithstanding anything contained herein to the contrary,
     Lessor shall have absolutely no obligation to perform any construction in
     the Subleased Premises.
     
     (b)  If Lessor succeeds to the rights of Sublessor under the Sublease,
upon cancellation or surrender or termination of the Overlease, Sublessee will
attorn to and recognize and be bound to Lessor as landlord under the Sublease,
and, provided that Sublessee is not then in default under the Sublease beyond
all applicable periods of grace and cure thereunder, Lessor will accept such
attornment and recognition, for the unexpired term of the Sublease, subject to
all of the terms of the Sublease and of this Consent, and the Sublease shall
continue in full force and effect, without the necessity of executing any new
document, as a direct lease between Sublessee and Lessor.  Nevertheless,
Sublessee shall, from time to time, execute and deliver such instruments
evidencing such attornment as Lessor may require.

     5.   Lessor shall not in any manner be deemed to have assumed or
undertaken any obligation or responsibility of any nature to Sublessee, and
Sublessee hereby covenants and agrees to look solely to Sublessor for
satisfaction of any claim, demand or liability of any nature in any manner
arising out of or relating to the Sublease or Sublessee's occupancy of the
subleased premises.

     6.   Sublessor hereby covenants and agrees to protect, indemnify and save
harmless, to the fullest extent permitted by law, Lessor and its officers,
trustees, employees, agents, and servants or holders of mortgages on the Leased
Premises (hereinafter the "Indemnified Parties") from and against any and all
liabilities, costs, expenses, causes of action, injuries, accidents,
injunctions, losses, claims, 





                                      83

<PAGE>   13

damages, suits, actions, demands, judgments, fines or penalties or any nature
whatsoever including reasonable attorney's fees and costs of litigation
commenced by or on behalf of any person, party or governmental authority
whatsoever (a) in any manner arising out of or relating to the Sublease or
Sublessee's occupancy of the subleased premises, (b) arising out of or in any
manner relating to any act, fault, omission, negligence or misconduct of
Sublessee or any of its representatives, employees, agents, servants or
contractors, (c) arising out of or in any manner relating to any breach
or default by Sublessee in the performance of any of its obligations under the
Sublease and/or this Consent or (d) arising out of or in any manner relating to
any injury to or death of any person or damage to or loss of property or any
matter or thing occurring in the subleased premises or arising out of any
condition in the subleased premises no matter how caused.  This indemnity
agreement shall include indemnity against all costs, claims, expenses,
liabilities, penalties and liens, including without limitation, court costs and
reasonable attorney's fees, incurred in connection with any such claim or
proceedings brought thereon, and the defense thereof.  In case any action or
proceeding is brought against any of the Indemnified Parties by reason or any
such claim, Sublessor, upon notice from Lessor, and at Lessor's option, shall
resist or defend such action or proceeding with counsel approved by Lessor.

     7.   Sublessee hereby covenants and agrees to perform and observe the
terms and conditions to be performed on the part of Sublessor under the
provisions of the Overlease with respect to the subleased premises as provided
in the Sublease, and Sublessee shall not do or permit to be done anything
whatsoever which violates the terms and conditions of the Overlease.
     8.   Notwithstanding anything to the contrary contained herein, neither
this Consent nor the Sublease shall in any manner be deemed to amend, modify or
alter any of the terms or conditions of the Overlease; and the consent of
Lessor to the Sublease, as set forth herein, shall in no manner be deemed to be
a waiver of the restrictions of the Overlease as to any future assignment,
subletting or permission to use or occupy all or any portion of the Leased
Premises on any occasion subsequent hereto.  Further, the Sublease shall not be
amended or modified in any respect, nor, except as provided in Paragraph 2.2 of
the Sublease, may the term thereof be extended, without the prior written
consent of Lessor.

     9.   Neither this Consent nor any provision hereof may be waived,
modified, amended, discharged or terminated, except by an instrument in writing
signed by the party against which the enforcement of any such waiver,
modification, amendment, discharge or termination is sought, and then only to
the extent set forth in such instrument.

     10.  This Consent shall be construed in accordance with and governed by
the laws of the Commonwealth of Massachusetts.

     11.  All covenants, agreements, conditions and undertakings as contained
in this Consent shall extend to and be binding upon the legal representatives,
successors and permitted assigns of each of the respective parties hereto.

     12.  Each party hereby represents and warrants to the others that it has
the full right, power and authority to enter into this Consent (and, as to
Sublessor and Sublessee, to enter into the Sublease), and to perform all of
their respective obligations thereunder, and that the person signing this
Consent (and, as to Sublessor and Sublessee, the Sublease) on its behalf has
the requisite lawful authority to do so.

     IN WITNESS WHEREOF, the parties have caused this Consent to Sublease and
Agreement to be duly executed as of the day and year first above written,
intending this document to take effect as a sealed instrument.





                                      84

<PAGE>   14
WITNESS:                          LESSOR:

                                  MASSACHUSETTS INSTITUTE OF TECHNOLOGY



 /s/PATRICIA D. MCKENZIE          By:  /s/PHILIIP A. TRUSSELL
- ------------------------------        ------------------------------------------
                                      Name:  Philip A. Trussell
                                      Title: Director of Real Estate, Associate 
                                             Treasurer
                                      Hereunto Duly Authorized


                                  
                                  SUBLESSOR:

                                  IMMUNOGEN, INC.



/s/CHERYL D. LINEHAN              By:  /s/FRANK J. POCHER
- ------------------------------        ------------------------------------------
                                      Name:  Frank J. Pocher
                                      Title: Vice President
                                      Hereunto Duly Authorized


                                  SUBLESSEE:

                                  ASTRA RESEARCH CENTER BOSTON, INC.



/s/REGINA A. LANDERS              By:  /s/HANS G. NILSSON
- ------------------------------        ------------------------------------------
                                      Name:  Hans G. Nilsson
                                      Title: President
                                      Hereunto Duly Authorize









                                      85



<PAGE>   1
                                                                Exhibit 10.26

                              AMENDMENT TO LEASE
                                       
     Agreement made this 31st day of August, 1995 between Massachusetts
Institute of Technology, Treasurer's Office, Suite 200, 238 Main Street,
Cambridge, MA 02142 ("Lessor") and ImmunoGen, Inc., 128 Sidney Street,
Cambridge, MA 02139 ("Lessee").  Unless otherwise defined herein capitalized
terms shall have the meaning set forth in the Lease as defined below.

     WHEREAS, Lessor and Lessee are parties to a lease agreement for the land
and building known as 128 Sidney Street, Cambridge, Massachusetts dated
December 23, 1992 (the "Lease");

     WHEREAS, Lessor and Lessee desire to amend the Lease to by deleting
Lessee's right to borrow from Lessor the cost of certain improvements made to
the Premises by the Lessee and to increase Lessee's share of profit from a
sublease of the Premises to take into account the Lessee's investment in such
improvements;

NOW, THEREFORE, the parties agree as follows:

     1.   Section 3.1(b) is revised to read as follows:

          (b)  All other costs, charges, or expenses which
               Lessee in this Lease agrees to pay or which Lessor pays or
               incurs as the result of a default by Lessee hereunder, including
               any penalty or interest which may be added for nonpayment or
               late payment thereof as provided in this
 Lease (collectively,
               "Additional Rent").
               
     2.   Section 8.0(c) is revised to read as follows:
               
          (c)  If Lessor consents to an assignment or sublease:
               (i) Lessee shall promptly deliver to Lessor a fully executed
               copy of said assignment or sublease; (ii) Lessee shall remain
               primarily liable to Lessor hereunder (which liability shall be
               joint and several with the assignee or sublessee); and (iii) if
               the aggregate rent and other amounts payable to Lessee under or
               in connection with such assignment or sublease, after deduction
               of the cost of Lessee's Work amortized on a straight-line basis
               over the Initial Lease Term, and the costs reasonably incurred
               by Lessee in entering into such assignment or sublease
               (including, without limitation, reasonable attorneys' fees and
               expenses, brokerage commissions, and alterations costs amortized
               on a straight-line basis over the term of such sublease),
               exceeds the Rent payable hereunder, Lessee shall pay to Lessor,
               as Additional Rent, one-half (1/2) of the amount of such excess
               immediately upon receipt thereof by Lessee.
               
               The parties agree that for the purposes of this
               Section 8.0(c) the cost of Lessee's Work is $8.91 per rentable
               square foot, but for purposes of this sublease of even date to
               be entered into by Lessee, as sublessor and ASTRA Research
               Center Boston, Inc., as sublessee, the cost of Lessee's Work
               shall be capped at $5.95 per rentable square foot, which will
               result in there being due to Lessor as Additional Rent during
               the term of such sublease an amount equal to $3.50 per rentable
               square foot during the initial term thereof and not less than
               $3.50 per rentable square foot during the extension term thereof
               (if said sublease is so extended).





                                      87

<PAGE>   2
     3.   Section 13.5(b) is revised to read as follows:
               
          (b)  Lessee shall diligently act to repair and restore
               the remainder of the Premises, including without limitation,
               "Lessee's Work" (as defined in the Work Letter), and all
               Alterations made by Lessee (or, in the case of a taking, what
               remains thereof), to substantially the condition in which they
               existed prior to the occurrence of such taking or casualty,
               PROVIDED, HOWEVER, that:  (i) Lessee shall not be required to
               replicate Lessee's Work and all Alterations as they existed
               immediately prior to such casualty, but the plans and
               specifications for Lessee's repair and restoration shall be
               subject to Lessor's reasonable approval as provided in the Work
               Letter; (ii) the provisions of Sections 1, 2, 3, 4, 5, 6 and 8
               of the Work Letter shall apply to such repair; (iii) in the
               event that the amount of insurance proceeds available for the
               repair and restoration work of both Lessor and Lessee hereunder
               from the insurance policy maintained by Lessee pursuant to
               Section 7.2 above is reduced by reason of the fact that Lessor
               has maintained insurance with respect to the Premises concurrent
               in coverage with the insurance maintained by Lessee pursuant to
               Section 7.2, Lessor shall provide the funds necessary to make up
               such deficit; and (iv) promptly upon completion of its work
               under this clause (b), Lessee shall diligently act to restore
               and/or replace all of Lessee's Property to substantially the
               same condition they were in prior to the occurrence of such
               taking or casualty.  Lessee shall give Lessor written notice of
               the date on which Lessee commences such repair or restoration
               work.
               
     4.   Section 27.2 is deleted in its entirety.

     5.   The Work Letter attached to the Lease as Exhibit D is revised as 
          follows:
               
          (a)  The definitions of "Lessee's Amortization Payments" and "Lessor's
               Allowance" are deleted from Paragraph 1.
               
          (b)  The first subparagraph of Paragraph 2 is revised to read as 
               follows:
                              
               Subject to the provisions of Section 18.2 of the
               Lease, Lessor is leasing the Premises to Lessee in its "as is"
               condition, and Lessor shall have no obligation to perform any
               repairs or make any improvements to the Premises in anticipation
               of Lessee's occupancy thereof.  Lessee shall perform Lessee's
               Work at Lessee's sole cost and expense.
               
          (c)  The first subparagraph of Paragraph 3 is revised to read as 
               follows:
               
               Lessee shall be solely responsible for the
               preparation and completion of all preliminary and final Working
               Drawings.  Lessee shall retain its own architects and engineers
               to prepare Working Drawings, provided that Lessor first approves
               such engineers and architects so selected by Lessee, which
               approval shall not be unreasonably withheld or delayed.  Lessee
               shall provide copies of the preliminary Working Drawings to
               Lessor, and Lessor shall provide to Lessee within fifteen (15)
               business days thereafter a list of corrections and modifications
               which Lessor requires to be made to the Working Drawings so as
               to make the Working Drawings consistent with the base Building
               systems and to 





                                      88

<PAGE>   3

               provide that the Lessee's Work is of a type capable of
               being reused by a typical research and laboratory user. 
               Lessor shall also provide to Lessee within such 15-business day
               period a list of those elements of Lessee's Work which Lessee
               must remove at the expiration or earlier termination of this
               Lease.
               
          (d)  The third sentence of the second paragraph of Paragraph 3 is 
               revised to read as follows:
               
               Lessor shall also provide to Lessee within such
               15-business day period a supplementary list of those elements of
               Lessee's Work which Lessee must remove at the expiration or
               earlier termination of this Lease (if any).
          
          (e)  Paragraph 9 is deleted in its entirety.
               
     In all other respects, the terms and provisions of the Lease are hereby
ratified and confirmed and remain in full force and effect and unamended.

     EXECUTED UNDER SEAL as of the date set forth above.


     Lessor:                  MASSACHUSETTS INSTITUTE OF TECHNOLOGY



                              By:    /s/PHILIP A. TRUSSELL
                                  ------------------------------------------
                                     Name:  Philip A. Trussell
                                     Title: Director of Real Estate, Associate 
                                            Treasurer
                                     Hereunto duly authorized




     Lessee:                  IMMUNOGEN, INC.



                              By:    /s/FRANK J. POCHER
                                  ------------------------------------------
                                     Name:  Frank J. Pocher
                                     Title:   Vice President
                                     Hereunto duly authorized










                                      89



<PAGE>   1

                                                                Exhibit 10.27

                                   DEBENTURE
                                       
     NEITHER THESE SECURITIES NOR THE SECURITIES ISSUABLE UPON CONVERSION
HEREOF HAVE BEEN REGISTERED WITH THE UNITED STATES SECURITIES AND EXCHANGE
COMMISSION OR THE SECURITIES COMMISSION OF ANY STATE OR UNDER THE SECURITIES
ACT OF 1933, AS AMENDED.  THE SECURITIES ARE RESTRICTED AND MAY NOT BE OFFERED,
RESOLD, PLEDGED OR TRANSFERRED EXCEPT IN ACCORDANCE WITH REGULATION S UNDER THE
ACT, OR AS PERMITTED UNDER THE ACT PURSUANT TO REGISTRATION OR EXEMPTION
THEREFROM AS EVIDENCED BY AN OPINION (WHICH SHALL BE IN FORM AND SUBSTANCE
SATISFACTORY TO THE COMPANY) OF COUNSEL SATISFACTORY TO THE COMPANY, THAT SUCH
REGISTRATION IS NOT REQUIRED.

No. 5AUS                           $350,000
                               IMMUNOGEN, INC.
           7% SUBORDINATED CONVERTIBLE DEBENTURE DUE July 31, 1996

     THIS DEBENTURE is one of a duly authorized issue of Debentures of
IMMUNOGEN, INC., a corporation duly organized and existing under the laws of
the Commonwealth of Massachusetts (the "Company"), designated as its 7%
Convertible Debenture Due July 31, 1996.

     FOR VALUE RECEIVED, the Company promises to pay to BARRAS INVESTMENTS
INC., the registered holder hereof (the "Holder"), the principal sum of THREE
HUNDRED FIFTY THOUSAND DOLLARS (US $350,000) on July 31, 1996 (the "Maturity

Date") and to pay interest on the principal sum outstanding from time to time
in arrears on July 31, 1996, at the rate of 7% per annum accruing from the date
of initial issuance.  Accrual of interest shall commence on the first such
business day to occur after the date hereof until payment in full of the
principal sum has been made or duly provided for.  All interest so payable will
be paid to the person in whose name this Debenture (or one or more predecessor
Debentures) is registered on the records of the Company regarding registration
and transfers of the Debentures (the "Debenture Register") on the tenth day
prior to the Maturity Date; provided, however, that the Company's obligation to
a transferee of this Debenture arises only if such transfer, sale or other
disposition is made in accordance with the terms and conditions of the
Regulation S Subscription Agreement executed by the original Holder.  The
principal of, and interest on, this Debenture are payable in such coin or
currency of the United States of America as at the time of payment is legal
tender for payment of public and private debts, at the address last appearing
on the Debenture Register of the Company as designated in writing by the Holder
from time to time.  The Company will pay the principal of and interest upon
this Debenture on the Maturity Date, less any amounts required by law to be
deducted, to the registered holder of this Debenture as of the tenth day prior
to the Maturity Date and addressed to such holder as the last address appearing
on the Debenture Register.  The forwarding of such check shall constitute a
payment of interest hereunder and shall satisfy and discharge the liability for
principal and interest on this Debenture to the extent of the sum represented
by such check plus any amounts so deducted.

   This Debenture is subject to the following additional provisions:

     1.   The Debentures are issuable in denominations of Fifty Thousand
Dollars (US $50,000) and integral multiples thereof.  The Debentures are
exchangeable for an equal aggregate principal amount of Debentures of different
authorized denominations, as requested by the Holders surrendering the same.
No service charge will be made for such registration or transfer or exchange.





                                      91

<PAGE>   2
    2.   The Company shall be entitled to withhold from all payments of
principal of, and interest on, this Debenture any amounts required to be
withheld under the applicable provisions of the United States income tax laws
or other applicable laws at the time of such payments, and Holder shall execute
and deliver all required documentation in connection therewith.

     3.   This Debenture has been issued subject to investment representations
of the original purchaser hereof and may be transferred or exchanged only in
compliance with the Securities Act of 1933, as amended (the "Act"), and other
applicable state and foreign securities laws.  In the event of any proposed
transfer of this Debenture, the Company may require, prior to issuance of a new
Debenture in the name of such other person, that it receive reasonable transfer
documentation including opinions that the issuance of the Debenture in such
other name does not and will not cause a violation of the Act or any applicable
state or foreign securities laws.   Prior to due presentment for transfer of
this Debenture, the Company and any agent of the Company may treat the person
in whose name this Debenture is duly registered on the Company's Debenture
Register as the owner hereof for the purpose of receiving payment as herein
provided and for all other purposes, whether or not this Debenture be overdue,
and neither the Company nor any such agent shall be affected by notice to the
contrary.

    4.   The Holder of this Debenture is entitled, at its option, to convert at
any time commencing on forty-five (45) days after the closing of the sale of
the entire series of Debentures of which this Debenture is a part until
maturity hereof, all or a portion of the principal amount of this Debenture,
provided the principal amount converted is at least US $50,000 (unless if at
the time of such election to convert the aggregate principal amount of all
Debentures registered to the Holder is less than Fifty Thousand Dollars (US
$50,000), then the whole amount thereof), into shares of Common Stock of the
Company at a conversion price for each share of Common Stock equal to
Seventy-Five Percent (75%) of the Market Price of the Company's Common Stock
per share.  For purposes of this Section 4, the Market Price shall be the
closing price of the Common Stock on the trading day immediately preceding the
conversion date as reported by the National Association of Securities Dealers
Automated Quotation System ("NASDAQ"), or the  closing bid price on the
over-the-counter market on such date or, in the event the Common Stock is
listed on a stock exchange, the Market Price shall be the  closing price on the
exchange on such date, as reported in the Wall Street Journal.  Such conversion
shall be effectuated by surrendering the Debentures to be converted to the
Company with the form of conversion notice attached hereto as Exhibit A,
executed by the Holder of the Debenture evidencing such Holder's intention to
convert this Debenture or a specified portion (as above provided) hereof, and
accompanied, if required by the Company, by proper assignment hereof in blank.
Interest accrued or accruing from the date of issuance to the date of
conversion shall be paid upon conversion by issuance of shares of Common Stock
of the Company, at the Market Price.  No fraction of Shares or scrip
representing fractions of shares will be issued on conversion, but the number
of shares issuable shall be rounded to the nearest whole share.  The date on
which notice of conversion is given shall be deemed to be the date on which the
Holder has delivered this Debenture, with the conversion notice duly executed,
to the Company or, if earlier, the date of receipt of such notice of conversion
if the Debenture is received by the Company within three (3) business days
therefrom.  Facsimile delivery of the conversion notice shall be accepted by
the Company.  Certificates representing Common Stock upon conversion will be
delivered within five (5) business days from the date the notice of conversion
is delivered to the Company.

   5.   Notwithstanding the foregoing, the Company shall not be required to
convert the Debentures, or any portion thereof, to the extent that as a
consequence of such conversion, together with all prior conversions of
Debentures issued simultaneously herewith, the Company would be required to
issue more than 19.99% of the outstanding shares of Common Stock on the date of
issuance of the issued Debentures issued simultaneously herewith (as reported
in the Company's most recent SEC report) upon 





                                      92

<PAGE>   3

such conversion, without the approval of the holders of the Common Stock.  The
Company shall promptly notify all holders of Debentures in writing in the event
that the Company can no longer convert any such Debentures, and in such event
the Company shall, at the request of a majority of holders, either call a
shareholders meeting to seek the approval required and shall use its reasonable
best efforts to obtain such shareholder approval, or redeem the Debentures that
it cannot convert in accordance with and upon the terms hereof, within ten (10)
days after delivery of a request for redemption.

    6.   No provision of this Debenture shall alter or impair the obligation of
the Company, which is absolute and unconditional, to pay the principal of, and
interest on, this Debenture at the time, place, and rate, and in the coin or
currency, herein proscribed.  This Debenture and all other Debentures now or
hereafter issued of similar terms are direct obligations of the Company.  This
Debenture ranks equally with all other Debentures now or hereafter issued under
the terms set forth herein.

     7.   No recourse shall be had for the payment of the principal of, or the
interest on, this Debenture, or for any claim based hereon, or otherwise in
respect hereof, against any incorporator, shareholder, officer or director, as
such, past, present or future, of the Company or any successor corporation,
whether by virtue of any constitution, statute or rule of law, or by the
enforcement of any assessment or penalty or otherwise, all such liability
being, by the acceptance hereof and as part of the consideration for the issue
hereof, expressly waived and released.

    8.   If the Company merges or consolidates with another corporation or
sells or transfers all or substantially all of its assets to another person and
the holders of the Common Stock are entitled to receive stock, securities or
property in respect of or in exchange for Common Stock, then as a condition of
such merger, consolidation, sale or transfer, the Company and any such
successor, purchaser or transferee shall amend this Debenture to provide that
it may thereafter be converted on the terms and subject to the conditions set
forth above into the kind and amount of stock, securities or property
receivable upon such merger, consolidation, sale or transfer by a holder of the
number of shares of Common Stock into which this Debenture might have been
converted immediately before such merger, consolidation, sale or transfer,
subject to adjustments which shall be as nearly equivalent as may be
practicable.  In the event of any proposed merger, consolidation or sale or
transfer of all or substantially all of the assets of the Company (a "Sale"),
the Holder hereof shall have the right to convert by delivering a Notice of
Conversion to the Company within fifteen (15) days of receipt of notice of such
Sale from the Company.  In the event the Holder hereof shall elect not to
convert, the Company may prepay all outstanding principal and accrued interest
on this Debenture, less all amounts required by law to be deducted, upon which
tender of payment following such notice, the right of conversion shall
terminate.

    9.   The Holder of the Debenture, by acceptance hereof, agrees that this
Debenture is being acquired for investment and that such Holder will not offer,
sell or otherwise dispose of this Debenture or the Shares of Common Stock
issuable upon conversion thereof except under circumstances which will not
result in a violation of the Act or any applicable state Blue Sky or foreign
laws or similar laws relating to the sale of securities.

     10.      This Debenture shall be governed by and construed in accordance
with the laws of the Commonwealth of Massachusetts.

     11.  The following shall constitute an "Event of Default":

         a.   The Company shall default in the payment of principal or interest
on this Debenture; or





                                      93

<PAGE>   4
         b.   Any of the representations or warranties made by the Company
herein, in the Subscription Agreement, or in any certificate or financial or
other written statements heretofore or hereafter furnished by or on behalf of
the Company in connection with the execution and delivery of this Debenture or
the Subscription Agreement shall be false or misleading in any material respect
at the time made; or

          c.   The Company shall fail to perform or observe, in any material
respect, any other covenant, term, provision, condition, agreement or
obligation of the Company under this Debenture and such failure shall continue
uncured for a period of thirty (30) days after notice from the Holder of such
failure; or

         d.   The Company shall (1)  admit in writing its inability to pay its
debts generally as they mature; (2) make an assignment for the benefit of
creditors or commence proceedings for its dissolution; or (3) apply for or
consent to the appointment of a trustee, liquidator or receiver for its or for
a substantial part of its property or business; or

          e.   A trustee, liquidator or receiver shall be appointed for the
Company or for a substantial part of its property or business without its
consent and shall not be discharged within sixty (60) days after such
appointment; or

         f.   Any governmental agency or any court of competent jurisdiction at
the instance of any governmental agency shall assume custody or control of the
whole or any substantial portion of the properties or assets of the Company and
shall not be dismissed within sixty(60) days thereafter; or

         g.   Any money judgment, writ or warrant of attachment, or similar
process in excess of  Two Hundred Thousand ($200,000) Dollars in the aggregate
shall be entered against the Company or any of its properties or other assets
and shall remain unpaid, unvacated, unbonded or unstayed for a period of sixty
(60) days or in any event later than five (5) days prior to the date of any
proposed sale thereunder; or

          h.   Bankruptcy, reorganization, insolvency or liquidation
proceedings or other proceedings for relief under any bankruptcy law or any law
for the relief of debtors shall be instituted by or against the Company and, if
instituted against the Company, shall not be dismissed within sixty (60) days
after such institution or the Company shall by any action or answer approve of,
consent to, or acquiesce in any such proceedings or admit the material
allegations of, or default in answering a petition filed in any such
proceeding; or

         i.   The Company shall have its Common Stock delisted from an exchange
or over-the-counter market or suspended from trading; provided that a change in
the listing of the Common Stock from NASDAQ/NMS to the NASDAQ SmallCap Market
will not constitute a default hereunder.
Then, or at any time thereafter, and in each and every such case, unless such
Event of Default shall have been waived in writing by the Holder (which waiver
shall not be deemed to be a waiver of any subsequent default) at the option of
the Holder and in the Holder's sole discretion, the Holder may consider this
Debenture immediately due and payable, without presentment, demand, protest or
notice of any kinds, all of which are hereby expressly waived, anything herein
or in any note or other instruments contained to the contrary notwithstanding,
and the Holder may immediately, and without expiration of any period of grace,
enforce any and all of the Holder's rights and remedies provided herein or any
other rights or remedies afforded by law.





                                      94

<PAGE>   5

     12.  Nothing contained in this Debenture shall be construed as conferring
upon the Holder the right to vote or to receive dividends or to consent or
receive notice as a shareholder in respect of any meeting of shareholders or
any rights whatsoever as a shareholder of the Company, unless and to the extent
converted in accordance with the terms hereof.

     13.  The Company and each Holder of this Debenture covenant and agree that
the payment of the principal of and interest on this Debenture shall be
subordinated in right of payment to the prior payment in full in cash of all of
the Company's indebtedness or obligations of any kind whatsoever outstanding
from time to time that is not expressly designated as subordinated indebtedness
(the "Senior Debt").  In the event of any insolvency, bankruptcy or similar
proceedings relative to the Company or to its property, then:

     a.   the holders of Senior Debt shall be entitled to receive payment in
full in cash of all amounts due on or in respect of all Senior Debt before the
Holder of this Debenture is entitled to receive any payment or distribution of
any kind or character on account of this Debenture;

     b.   any payment or distribution by the Company of any kind or
character to which the Holder of this Debenture would be entitled but for the
provisions of this Section shall be paid, ratably, directly to the holders of
Senior Debt or their representative or representatives; and

     c.   in the event that, notwithstanding the foregoing, the Holder of
this Debenture shall have received any payment or distribution  by the
Company of any kind or character, from and after the date of any such event set
forth above before all Senior Debt is paid in full in cash, then and in such
event such payment or distribution shall be paid over or delivered forthwith to
the trustee in bankruptcy or other person or entity making payment or
distribution of assets of the Company for application to the payment of all
Senior Debt remaining unpaid.

     In case any payment or distribution shall be paid or delivered to any
Holder of this Debenture in violation or contravention of the terms of this
Section, such payment or distribution shall, upon such Holder's receipt of
notice of such violation or contravention, be held in trust for and paid and
delivered ratably to the holders of Senior Debt (or their duly authorized
representatives), until all Senior Debt shall have been paid in full.

     IN WITNESS WHEREOF, the Company has caused this instrument to be duly
executed by an officer thereunto duly authorized.

Dated: __________________________           IMMUNOGEN, INC.

                                            By: /S/MITCHEL SAYARE
                                               -----------------------------
                                                Mitchel Sayare
                                                Chief Executive Officer





                                      95

<PAGE>   6
EXHIBIT A

NOTICE OF CONVERSION
(To be Executed by the Registered Holder in order to Convert the Debenture)

     The undersigned hereby irrevocably elects to convert $ ________________ of
the principal amount of the above Debenture No. ___ into Shares of Common Stock
of IMMUNOGEN, INC. (the "Company") according to the conditions hereof, as of
the date written below.

     The undersigned represents that it is not a U.S. Person as defined in
Regulation S promulgated under the Securities Act of 1933, is not converting
the Debenture on behalf of any U.S. Person and is converting the Debenture
outside of the United States and will receive the shares of Common Stock
issuable upon conversion outside of the United States.

Date of Conversion* ___________________________________________________________

Applicable Conversion Price ___________________________________________________

Signature _____________________________________________________________________
            [Name]

Address: ______________________________________________________________________
  _____________________________________________________________________________







* This original Debenture and Notice of Conversion must be received by the
Company by the fifth business day following the Date of Conversion.








                                      96

<PAGE>   7


<TABLE>
IMMUNOGEN, INC.

<CAPTION>
DEBENTURE HOLDER                         AMOUNT                CONVERSION DATE
- ----------------                         ------                ---------------
<S>                                     <C>                       <C>
FTS Worldwide Corp.                     $350,000                  10/02/95
Euro Factors International, Inc.         250,000                  10/02/95
Siata Holding Corp.                      350,000                  10/02/95
Nepo Invest Trade                        500,000                  10/02/95
Barras Investments Inc.                  350,000                  10/02/95

FTS Worldwide Corp.                      350,000                  10/18/95
Euro Factors International, Inc.         250,000                  10/18/95
Siata Holding Corp.                      350,000                  10/18/95
Nepo Invest Trade                        500,000                  10/18/95
Barras Investments Inc.                  350,000                  10/18/95


</TABLE>















                                      97




<PAGE>   1
                                                                Exhibit 10.28

                                   EXHIBIT A
                  OFFSHORE SECURITIES SUBSCRIPTION AGREEMENT
                                       
     This Offshore Securities Subscription Agreement ("Agreement") is executed
in reliance upon the transaction exemption afforded by Regulation S
("Regulation S") as promulgated by the Securities and Exchange Commission
("SEC"), under the Securities Act of 1933, as amended ("1933 Act").

     This Agreement has been executed by the undersigned in connection with the
private placement of 7% Convertible Debentures (hereinafter referred to as the
"Debentures") of ImmunoGen, Inc., a corporation organized and existing under
the laws of the Commonwealth of Massachusetts, U.S.A., NASDAQ National Market
Symbol "IMGN" (hereinafter referred to as the "COMPANY").  The Debentures being
sold pursuant to this Agreement, and the Shares (as defined below), have not
been registered under the 1933 Act and may not be offered or sold in the United
States or to U.S. Persons, other than distributors (as such terms are defined
in Regulation S), unless the Debentures or the Shares, as the case may be, are
registered under the 1933 Act, or an exemption from the registration provisions
of the 1933 Act is available.  The terms on which the Debentures may be
converted into common stock (the "Shares")
 and the other terms of the
Debentures are set forth in the pro forma Debenture in Annex I annexed hereto.
This subscription and, if accepted by the COMPANY, the offer and sale of
Debentures and the Shares issuable upon conversion thereof (collectively the
"Securities"), are being made in reliance upon the provisions of Regulation S
("Regulation S") under the 1933 Act.

     The undersigned

NAME:
ADDRESS:


if applicable, a [Corporation][Partnership][Trust] organized under the laws of
__________, a non USA jurisdiction (hereinafter referred to as the "PURCHASER")
hereby represents and warrants to, and agrees with, the COMPANY as follows:

     1.   Agreement to Subscribe.

    a.   Subscription Amount.  The undersigned hereby subscribes for
$______________  in principal amount of 7% Debentures.

    b.   Form of Payment.  The PURCHASER shall pay the purchase price for the
Debentures by delivering good funds in United States Dollars to the escrow
agent identified in the Joint Escrow Instructions attached hereto as Annex II
(the "Escrow Agent").  Delivery of such funds to the COMPANY by the Escrow
Agent shall be made against delivery by the COMPANY of one or more
Debentures in accordance with this Agreement.  By signing this Agreement, the
PURCHASER and the COMPANY each agrees to all of the terms and conditions of,
and becomes a party to, the Joint Escrow Instructions attached hereto as Annex
II, all of the provisions of which are incorporated herein by this reference as
if set forth in full.

     c.   Method of Payment.  Payment of the purchase price for the Debentures
shall be          made by wire transfer of funds to:





                                      99


<PAGE>   2
        Bank of New York        350 Fifth Avenue        New York, New York 10001

        ABA# 021000018

For Further Credit to A/C# 1050036843 for credit to the account of Krieger &
Prager, Attorneys
        Not later than three (3) business days after acceptance and execution
of this Agreement by the COMPANY, the PURCHASER shall deposit with the Escrow
Agent the aggregate subscription price for the Debentures.

     2.   Subscriber Representations and Covenants; Access to Information;
Independent Investigation.
          a.   Offshore Transaction.  PURCHASER represents, warrants and
covenants to COMPANY as follows:

            (i)  PURCHASER is not a U.S. Person as that term is defined under
Regulation S, as set forth in Annex III.

           (ii) PURCHASER is outside the United States as of the date of the
execution and delivery of this Agreement.

          (iii)     PURCHASER is purchasing the Debentures for its own account
and not on behalf of any U.S. Person, and PURCHASER is the sole beneficial
owner of the Debentures, and has not pre-arranged  any sale with any purchaser
or purchasers in the United States.

           (iv) PURCHASER represents and warrants and hereby agrees that all
offers and sales of the Debentures prior to the expiration of a period
commencing on the date of the receipt of funds by the COMPANY and
ending 40 days thereafter (the "Restricted Period") shall only be made in
compliance with the safe harbor contained in Regulation S, pursuant to the
registration provisions under the 1933 Act or pursuant to an exemption from
registration, and all offers and sales after the expiration of the 40-day
period shall be made only pursuant to such registration or to an exemption from
registration.

            (v)  PURCHASER acknowledges that the purchase of the Debentures
involves a high degree of risk is aware of the risks and further acknowledges
that it can bear the economic risk of the purchase of the Debentures, including
the total loss of its investment.

           (vi) PURCHASER understands that the Debentures are being offered and
sold to it in reliance on specific exemptions from the  registration
requirements of U.S. securities laws and that the COMPANY is relying upon the
truth and accuracy of the representations, warranties, agreements,
acknowledgments and understandings of PURCHASER set forth herein in order to
determine the applicability of such exemptions and the suitability of PURCHASER
to acquire the Debentures, and the Shares issuable upon conversion thereof.
PURCHASER represents and warrants that the information contained herein is
complete and  accurate.  PURCHASER further represents and warrants that it will
notify the COMPANY immediately upon the occurrence of any material change
therein occurring prior to the issuance of Shares upon conversion of the
Debenture.

          (vii)     PURCHASER is sufficiently experienced in financial and
business matters to be capable of evaluating the merits and risks of its
investments, and to make an informed decision relating thereto.




                                      100


<PAGE>   3
         (viii)    In evaluating its investment, PURCHASER has consulted its
own investment and/or legal and/or tax advisors.  PURCHASER is not relying on
the COMPANY respecting the tax and other economic considerations of an
investment in the Debentures.

           (ix)  PURCHASER understands that in the view of the SEC the statutory
basis for the exemption claimed for this transaction would not be present if
the offering of Debentures, and the Shares issuable  upon conversion thereof,
although in technical compliance with Regulation S, is part of a plan or scheme
to evade the registration provisions of the 1933 Act.  PURCHASER is acquiring
the Debentures for investment purposes and has no present intention to sell the
Debentures, or the Shares issuable upon conversion thereof, in the United
States or to a U.S. Person or for the account or benefit of a U.S. Person
either now or after the expiration of the Restricted Period.

           (x)  PURCHASER is not an underwriter of, or dealer in, the
Securities, and PURCHASER is not participating, pursuant to a contractual
agreement, in the distribution of the Securities.

           (xi)     During the period the Debenture is outstanding, neither
PURCHASER  nor any of its affiliates will, directly or indirectly,  maintain
any short position in the securities of the COMPANY.

          (xii)     During the period  commencing on the Closing Date (as
defined herein) and ending on the 45th day following such date,  PURCHASER will
not sell, commit or agree to sell or pledge any shares of Common Stock of the
COMPANY or any other securities convertible into or exercisable for shares of
Common Stock of the COMPANY.

         (xiii)    PURCHASER has taken no action which would give rise to any
claim by any person for brokerage commission, finders' fees or the like
relating to this Agreement or the transactions contemplated hereby.

         b.   Current Public Information.  PURCHASER acknowledges that
PURCHASER has been furnished with or has acquired copies of the COMPANY's most
recent Annual Report on the Form 10-K filed with the SEC for the fiscal year
ended June 30, 1994, and the Forms 10-Q for the quarters ended September 30 and
December 31, 1994 and March 31, 1995, and 8-K filed thereafter (collectively
the "SEC Filings").  PURCHASER is not relying upon any representations or other
information (whether oral or written) other than as set forth in the SEC
filings or in Annex IV.

         c.   Independent Investigation; Access.  PURCHASER acknowledges that
PURCHASER, in making the decision to purchase the Debentures subscribed for,
has relied upon independent investigations made by it and its representatives,
if any, and PURCHASER and such representatives,       if any, have, prior to
any sale to it, been given access and the opportunity to examine all material
publicly available, books and records of the COMPANY, all material contracts
and documents relating to this offering and an opportunity to ask questions of,
and to receive answers from the COMPANY or any person acting on its behalf
concerning the terms and conditions of this offering.  PURCHASER and its
advisors, if any, have been furnished with access to all publicly available
materials relating to the business, finances and operation of the COMPANY and
materials relating to the offer and sale of the Debentures which have been
requested. PURCHASER and its advisors, if any, have received complete   and
satisfactory answers to any such inquiries.

         d.   No Government Recommendation or Approval.  PURCHASER understands
that no federal or state agency has passed on or made any recommendation or
endorsement of the Securities.




                                      101


<PAGE>   4
          e.   Entity Purchasers.  If PURCHASER is a partnership, corporation
or trust, the person executing this Agreement on its behalf represents and
warrants that:

              (i)  He or she has made due inquiry to determine the truthfulness
of the representations and warranties made pursuant to this Agreement.

              (ii) He or she is duly authorized (if the undersigned is a
trust, by the trust agreement) to make this investment and to enter into and
execute this Agreement on behalf of such entity.

          f.   Individual Purchasers.  PURCHASER, if an individual, represents
that he or she has reached the age of 21 and has adequate means for providing
for his or her current and anticipated financial needs and possible
contingencies for emergencies and has no need for liquidity in the proposed
investment.

          g.   Binding Commitment.  This Agreement constitutes a legal, valid
and binding obligation of the PURCHASER.  The PURCHASER has full power, right
and authority to enter into and perform this Agreement.  The execution and
delivery and performance of this Agreement will not violate or be in conflict
with any order, judgment, injunction, agreement or controlling document to
which the PURCHASER is a party or by which it is bound.  If the PURCHASER is an
entity, it was not formed for the specific purpose of acquiring the Debenture.

         h.   Foreign Laws.  PURCHASER hereby covenants that it will comply
with all laws and regulations in each foreign jurisdiction in which it
purchases, offers, sells or deliver the Securities, or has in its possession or
distributes any offering material.

     3.   COMPANY Representations.

          a.   Reporting Company Status.  The COMPANY is a reporting issuer as
defined by Rule 902 of Regulation S.  The COMPANY is in full compliance, to the
extent applicable, with all reporting obligations under either Section 12(b),
12(g) or 15(d) of the Securities Exchange Act of 1934, as amended (the
"Exchange Act").  The COMPANY has registered its common stock pursuant to
Section 12 of the Exchange Act and the common stock trades on NASDAQ/NMS.

          b.   Offshore Transaction.  The COMPANY has not offered these
securities to any person in the United States or to any U.S. Person as that
term is defined in Regulation S.

          c.   No Directed Selling Efforts.  In regard to this transaction, the
COMPANY has not conducted any "direct selling efforts" as that term is defined
in Rule 902 of Regulation S nor has the COMPANY conducted any general
solicitation relating to the offer and sale of the within securities to persons
resident within the United States or elsewhere.

          d.   Terms of Debentures.  The COMPANY will issue the Debentures in
accordance with the terms of Annex I attached hereto.

          e.   Legality.  The COMPANY has the requisite corporate power and
authority to enter into this Agreement and to sell and deliver the Debentures;
this Agreement and the issuance of the Debentures have been duly and validly
authorized by all necessary corporate action by the COMPANY; this Agreement has
been duly and validly executed and delivered by and on behalf of the COMPANY,
and is a valid and binding agreement of the COMPANY, enforceable against it in
accordance with its terms, 




                                      102


<PAGE>   5
except as enforceability may be limited by general equitable principles,
bankruptcy, insolvency, fraudulent conveyance, reorganization,  moratorium or
other laws affecting creditors rights generally.

          f.   Non-Contravention.  The execution and delivery of this Agreement
and the consummation of the issuance of the Debentures, and the consummation of
the transactions contemplated by this Agreement by the COMPANY do not and will
not conflict with or result in a breach by the COMPANY of any of the terms or
provisions of, or constitute a default under, the Articles of Organization or
by-laws of the COMPANY, or any material indenture, mortgage, deed of trust, or
other material agreement or instrument to which the COMPANY is a party or by
which it or any of its properties or assets are bound or (assuming that the
representations and warranties of the PURCHASER in Section 2 hereof, and the
representations and warranties of the distributor to the COMPANY, are true and
correct), any existing applicable U.S. law, rule, or regulation or any
applicable decrees, judgment or order of any U.S. court, federal or state
regulatory body, administrative agency or other U.S. governmental body having
jurisdiction over the COMPANY or any of its properties or assets, the conflict,
breach, violation or default of or under which would have a material adverse
effect on the COMPANY's business or financial condition.

          g.   Filings.  The COMPANY undertakes and agrees to make all
necessary filings in connection with the sale of the Debentures as required by
United States laws and regulations or any domestic securities exchange or
trading market.

          h.   Absence of Certain Changes.  Since March 31, 1995, there has
been no material adverse development in the assets, liabilities, business,
properties, operations, financial condition or results of operations of the
COMPANY, except as disclosed in the SEC Filings or in Annex IV.

    4.   Transfer Agent Instructions.

          a.   Debentures.  Upon the conversion of the Debentures, the
PURCHASER thereof shall submit such Debenture to COMPANY, and COMPANY shall,
within five (5) business days of receipt of such Debenture, instruct COMPANY's
transfer agent to issue one or more certificates representing that number of
shares of Common Stock into which the Debenture or Debentures are convertible
in accordance with the provisions regarding conversion set forth in Annex I
hereto.  The COMPANY shall act as Debenture Registrar and shall maintain an
appropriate ledger containing the necessary information with respect to each
Debenture.

          b.   Shares to be Issued Without Restrictive Legend.  Subject to the
completeness and accuracy of the PURCHASER's representations and warranties
herein, upon the conversion of any Debenture by a person who is a non-U.S.
Person, COMPANY shall instruct the COMPANY's transfer agent to issue stock
certificates without restrictive legend in the name of PURCHASER (or its nominee
(being a non-U.S. Person) or such non-U.S. Persons as may be designated by
PURCHASER prior to the closing) and in such denominations to be specified at
conversion representing the number of shares of Common Stock issuable upon such
conversion, as applicable; provided, however, that if the nominee or other
non-U.S. Person in whose name a certificate or certificates for shares are
requested to be registered is other than PURCHASER, or if there has been a
regulatory development including, but not limited to, an  amendment or proposed
amendment of Regulation S, or any "no-action" or interpretive guidance whether
oral or written from the Securities and Exchange Commission, which call into
question the ability of COMPANY to issue to PURCHASER the Securities without
registration under the United States Securities Act of 1933, COMPANY may require
prior to issuance of a certificate in the name of PURCHASER or such other
person, that it receive reasonable transfer documentation including 




                                      103


<PAGE>   6

opinions of counsel acceptable to COMPANY that the issuance of certificates
without restrictive legend and/or in such other name does not and will not cause
a violation of the Act or any applicable state or foreign securities laws; and
provided further that COMPANY warrants that no instructions other than these
instructions and instructions to impose a "stop transfer" instruction with
respect to the Debenture until the end of the Restricted Period have been or
will be given to the transfer agent and that the Shares will not be subject to  
any transfer limitations other than those imposed by applicable securities laws.
Nothing in this Section 4, however, shall affect in any way PURCHASER's or such
nominee's obligations and agreement to comply with all applicable securities
laws upon resale of the Securities.

         c.   If, solely as a result of the COMPANY's wrongful refusal to honor
PURCHASER's instruction in willful contravention of this Agreement, or wrongful
refusal or failure to transfer or issue the Shares in willful contravention of
this Agreement, PURCHASER suffers  any loss (other than any consequential,
indirect, incidental or special damages), the COMPANY shall reimburse PURCHASER
for such loss unless PURCHASER shall have breached any of its representations,
warranties or covenants set forth in this Agreement, or otherwise taken or
omitted to take actions, which actions or omissions constitute gross
negligence, bad faith or willful misconduct.

     5.   Exemption; Reliance on Representation.  PURCHASER understands that
the  offer and sale of the Debentures, and the Shares issuable upon conversion
thereof, is not being registered under the 1933 Act.  The COMPANY is relying on
the rules governing offers and sales made outside the United States pursuant to
Regulation S.  Rules 901 through 904 of Regulation S govern this transaction.

     6.   Closing Date and Escrow Agent.  The date of the issuance of the
Debentures and the sale of the Debentures as evidenced by receipt by the
COMPANY from the Escrow Agent or each PURCHASER's purchase funds (the "Closing
Date") shall be no later than ten (10) business days after execution hereof by
all parties or such other mutually agreed to time.  PURCHASER shall, within
three (3) business days after acceptance and execution of this Agreement by the
COMPANY, deliver the necessary funds as indicated in Paragraph 1 to the Escrow
Agent.  Debentures will be delivered to the Escrow Agent at the instructions of
the COMPANY.  PURCHASER agrees that the Escrow Agent has no liability as a
result of any fraudulent or unlawful conduct of any other party, and agrees to
hold the Escrow Agent harmless.

     7.   Conditions to the COMPANY's Obligation to Sell.  PURCHASER
understands that COMPANY's obligation to sell the Debentures is conditioned
upon:

          a.   The receipt and acceptance by the COMPANY of this Agreement as
evidenced by execution of this Agreement by the President or any Vice President
of the COMPANY.  The acceptance of funds by the COMPANY shall be deemed to be
constructive acceptance of this Agreement;

          b.   Delivery to the Escrow Agent by each PURCHASER of good funds as
payment in full for the purchase of the Debentures; and

          c.   The accuracy on the Closing Date of the representations and
warranties  of PURCHASER contained in this Agreement and the performance by
PURCHASER on or before the Closing Date of all covenants and agreements of
PURCHASER required to be performed on or before the Closing Date.

          d.   There shall not be in effect any law, rule or regulation
prohibiting or restricting the transactions contemplated hereby, or requiring
any consent or approval which shall not have been obtained.




                                      104


<PAGE>   7
      8.  Conditions to PURCHASER's Obligation to Purchase.  The COMPANY
understands that PURCHASER's obligation to purchase the Debentures is
conditioned upon:

          a.   Acceptance by PURCHASER of an Agreement for the sale of
Debentures;

          b.   Delivery of Debentures to Escrow Agent as herein set forth;

          c.   The accuracy on the Closing Date of the representations and
warranties of the COMPANY contained in this Agreement and the performance by
the COMPANY on or before the Closing Date of all covenants and agreements of
the COMPANY required to be performed on or before the Closing Date; and

          d.   Delivery to the Escrow Agent of an opinion of counsel for the
COMPANY, dated the Closing Date and addressed to PURCHASER, in the form
attached hereto as Annex III.

     9.   Registration of the Securities.  COMPANY hereby agrees that, upon
demand of a majority in interest of holders of the Securities as a result of a
regulatory development including, but not limited to, an amendment or proposed
amendment of Regulation S, or any "no-action" or interpretive guidance whether
oral or written from the Securities and Exchange Commission, which call into
question the ability of PURCHASER to resell the Securities without
registration, COMPANY will file, and use its reasonable best efforts to cause
to become effective a registration statement on Form S-3 under the 1933  Act
covering the resale of the Shares issuable upon conversion of the Debentures.
Any such registration statement shall remain effective for up to twelve (12)
months, or until all of the Securities are sold, whichever is earlier.  The
COMPANY shall provide the PURCHASER with such number of copies of the
prospectus as shall be reasonably requested to facilitate the sale of the
Shares issuable upon conversion of the Debentures.  The COMPANY shall bear and
pay all expenses incurred in connection with any such registration, excluding
discounts and commissions.

     10.  Further Offerings.  COMPANY agrees that, for a period of 180 days
from the Closing Date, it will not offer for sale or sell any securities other
than the Shares issuable upon conversion of the Debentures issued to the
PURCHASER and to other purchasers contemporaneously herewith, unless, in the
opinion of COMPANY's counsel, such offer or sale does not jeopardize the
availability of exemptions from the registration and qualification requirements
under all applicable securities laws with respect to the Shares.  COMPANY
hereby warrants that it has not engaged in any such offering during the six
months prior to the Closing Date, except as disclosed in Annex V hereof.

     11.  Governing Law.  This Agreement shall be governed by and construed
under the laws of the State of Massachusetts without giving effect to
principles governing the conflicts of laws.  A facsimile transmission of this
signed Agreement shall be legal and binding on all parties hereto.

     12.  Notices.  Any notice required or permitted hereunder shall be given
in writing (unless otherwise specified herein) and shall be deemed effectively
given upon personal delivery or three business days after deposit in the United
States Postal Service, by registered or certified mail with postage and fees
prepaid, addressed to each of the other parties thereunto entitled at the
following addresses, or at such other addresses as a party may designate by ten
days advance written notice to each of the other parties hereto.

COMPANY:  ImmunoGen, Inc.           148 Sidney Street        Cambridge, MA 02139
ATT: Chief Financial Officer





                                      105


<PAGE>   8

PURCHASER:  At the address set forth on the first page of this Agreement.
ESCROW AGENT: Krieger & Prager, Esqs. 319 Fifth Avenue  New York, New York 10016

     13.  Survival of Representations and Warranties.  PURCHASER's
representations and warranties shall survive the execution and delivery hereof
of t his Agreement and the delivery of the Debenture.

     14.  Each of the parties shall pay its own fees and expenses in connection
with this Agreement and the transactions contemplated hereby whether or not
consummated.

             SIGNATURE(S) FOR INDIVIDUAL SUBSCRIBER(S)

     IN WITNESS WHEREOF, the undersigned represents that the foregoing
statements are true and correct and that he, she or they have executed this
Offshore Securities Subscription Agreement this ______ day of ______________,
1995.


___________________________________  ____________________________________
Printed Name                          Signature

___________________________________  ___________________________________
Printed Name                          Signature

                            SIGNATURES FOR ENTITIES
                                       
     IN WITNESS WHEREOF, the undersigned represents that the foregoing
statements are true and correct and that it has caused this Offshore Securities
Subscription Agreement to be duly executed on its behalf this ________ day of
___________________, 1995.

             _____________________________________
            Printed Name of Subscriber


            By: _________________________________
                (Signature of Authorized Person)

             _____________________________________
            Printed Name and Title


Accepted this __________ day of the month of ___________________, 199___.


IMMUNOGEN, INC.


By: __________________________________________

Title: _______________________________





                                      106


<PAGE>   9

     All correspondence and delivery of certificates and confirmations should
be addressed to the above named person and sent by the COMPANY to his _____
business _____ home address (check one).

Capacity of Subscriber (check one):
                                                                               
Individual_______    Corporation_______    Partnership_______  Other___________ 
                                                                (please specify)


Ownership of Debentures (check one):

Individual __________     Joint Tenants, with right of survivorship__________*
Tenants in Common __________*     Tenants in Entirety  __________*
Community Property   __________*
Country of Citizenship:   ______________________________________________
Country of incorporation or formation: _________________________________

*    If you are purchasing Debentures with only your spouse as co-owner, both
you and your spouse must sign the signature page.  If any co-owner is not
your spouse, all co-owners must sign the signature page.

Name of PURCHASER Representative, if any: ___________________________________
          Address:                ___________________________________
                                  ___________________________________
          Telephone:              ___________________________________

Full Name and Address of PURCHASER for Registration Purposes:
NAME:       _______________________________________________________________
ADDRESS:    _______________________________________________________________
            _______________________________________________________________
            _______________________________________________________________
TEL. NO.    _______________________________________________________________
FAX. NO.    _______________________________________________________________
CONTACT NAME: _____________________________________________________________

Delivery Instructions (if different from Registration Name):

NAME:       _______________________________________________________________
ADDRESS:    _______________________________________________________________
            _______________________________________________________________
            _______________________________________________________________
TEL. NO.    _______________________________________________________________
FAX. NO.    _______________________________________________________________
CONTACT NAME: _____________________________________________________________

SPECIAL INSTRUCTIONS:
            _______________________________________________________________
            _______________________________________________________________
            _______________________________________________________________





                                      107




<PAGE>   1
                                       
                                                                    Exhibit 21
                                       
                                IMMUNOGEN, INC.
                                       
                        Subsidiaries of the Registrant
                                       
                                       
ImmunoGen Securities Corp.
Apoptosis Technology, Inc.













                                      109






<PAGE>   1

                                       
                                                                     EXHIBIT 23


CONSENT OF INDEPENDENT ACCOUNTANTS

We consent to the incorporation by reference in the registration statements of
ImmunoGen, Inc. on Form S-8 (File Nos. 33-41534 and 33-73544) of our report
dated September 1, 1995, on our audits of the consolidated financial statements
of ImmunoGen, Inc. as of June 30, 1995 and 1994, and for each of the three
years in the period ended June 30, 1995, which reports are included in the
Annual Report on Form 10-K.





                                        /s/ COOPERS & LYBRAND L.L.P.
                                        ------------------------------
                                        COOPERS & LYBRAND L.L.P.



Boston, Massachusetts
September 28, 1995







                                      111






<TABLE> <S> <C>

<ARTICLE> 5
       
<S>                             <C>
<PERIOD-TYPE>                   12-MOS
<FISCAL-YEAR-END>                          JUN-30-1995
<PERIOD-END>                               JUN-30-1995
<CASH>                                       3,047,236
<SECURITIES>                                         0
<RECEIVABLES>                                        0
<ALLOWANCES>                                         0
<INVENTORY>                                          0
<CURRENT-ASSETS>                             3,341,088
<PP&E>                                      23,851,069
<DEPRECIATION>                              10,229,686
<TOTAL-ASSETS>                              17,046,171
<CURRENT-LIABILITIES>                        4,466,978
<BONDS>                                              0
<COMMON>                                   119,114,522
<PREFERRED-MANDATORY>                                0
<PREFERRED>                                          0
<OTHER-SE>                                           0
<TOTAL-LIABILITY-AND-EQUITY>                17,046,171
<SALES>                                              0
<TOTAL-REVENUES>                               511,864
<CGS>                                                0
<TOTAL-COSTS>                                        0
<OTHER-EXPENSES>                            19,853,169
<LOSS-PROVISION>                                     0
<INTEREST-EXPENSE>                             509,700
<INCOME-PRETAX>                           (19,851,005)
<INCOME-TAX>                                     6,063
<INCOME-CONTINUING>                                  0
<DISCONTINUED>                                       0
<EXTRAORDINARY>                                      0
<CHANGES>                                            0
<NET-INCOME>                              (19,857,068)
<EPS-PRIMARY>                                   (1.58)
<EPS-DILUTED>                                   (1.58)
        

</TABLE>