UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 10-Q/A

Amendment No. 1

x                              QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934

For the quarterly period ended September 30, 2006

OR

o                                 TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934

For the transition period from            to                

Commission file number 0-17999

ImmunoGen, Inc.

128 Sidney Street, Cambridge, MA 02139

(Address of principal executive offices, including zip code)

(617) 995-2500

(Registrant’s telephone number, including area code)

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.      x Yes   o No

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, or a non-accelerated filer. See definition of “accelerated filer and large accelerated filer” in Rule 12b-2 of the Exchange Act. (Check one):

Indicate by check mark whether the registrant is a shell company (as defined in Rule 12b-2 of the Exchange Act).
o Yes   x No

Indicate the number of shares outstanding of each of the issuer’s classes of common stock, as of the latest practicable date.

Shares of common stock, par value $.01 per share:  41,541,834 shares outstanding as of November 1, 2006.

EXPLANATORY NOTE

This Amendment No. 1 to ImmunoGen, Inc.’s Quarterly Report Form 10-Q (“Form 10-Q”) for the quarter ended September 30, 2006, as filed with the U.S. Securities and Exchange Commission on November 3, 2006, is being filed solely to (i) revise Item 6 of Part II of the Form 10-Q to indicate that confidential portions of certain exhibits have been omitted and filed separately with the Commission pursuant to a confidentiality request and (ii) file appropriate certifications to accompany this Amendment No. 1 to the Form 10-Q.  With the exception of the foregoing, no other information in the Form 10-Q is being supplemented, updated or amended.

PART II.                      OTHER INFORMATION

ITEM 6.                             Exhibits.

+                    Previously filed.

++             Previously furnished.

*                    Certain confidential material contained in the document was omitted and filed separately with the SEC pursuant to Rule 24B-2 under the Securities Exchange Act of 1934, as amended.

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SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, as amended, the Registrant has duly caused this report to be signed on its behalf by the undersigned thereunto duly authorized.

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EXHIBIT INDEX

31.3                                                   Certification of Chief Executive Officer under Section 302 of the Sarbanes-Oxley Act of 2002.

31.4                                                   Certification of Principal Financial Officer under Section 302 of the Sarbanes-Oxley Act of 2002.

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EXHIBIT 31.3

CERTIFICATIONS

I, Mitchel Sayare, certify that:

1.     I have reviewed this Amendment No. 1 to the quarterly report on Form 10-Q of ImmunoGen, Inc.; and

2.     Based on my knowledge, this report does not contain any untrue statement of a material fact or omit to state a material fact necessary to make the statements made, in light of the circumstances under which such statements were made, not misleading with respect to the period covered by this report.

Date: August 7, 2007

EXHIBIT 31.4

CERTIFICATIONS

I, Daniel M. Junius, certify that:

1.     I have reviewed this Amendment No. 1 to the quarterly report on Form 10-Q of ImmunoGen, Inc.; and

2.     Based on my knowledge, this report does not contain any untrue statement of a material fact or omit to state a material fact necessary to make the statements made, in light of the circumstances under which such statements were made, not misleading with respect to the period covered by this report.

Date: August 7, 2007