<PAGE>


              As filed with the Securities and Exchange Commission
                              On December 18, 2001


                              Registration No. 33-


                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549


                                    FORM S-8
                             REGISTRATION STATEMENT

                                      UNDER

                           THE SECURITIES ACT OF 1933


                                 IMMUNOGEN, INC.
                                 ---------------
             (EXACT NAME OF REGISTRANT AS SPECIFIED IN ITS CHARTER)


        MASSACHUSETTS                                         04-2726691
        ----------------------------------------------------------------
(STATE OR OTHER JURISDICTION OF                            (I.R.S. EMPLOYER
INCORPORATION OR ORGANIZATION)                            IDENTIFICATION NO.)


                128 SIDNEY STREET, CAMBRIDGE, MASSACHUSETTS 02139
                -------------------------------------------------
                    (ADDRESS OF PRINCIPAL EXECUTIVE OFFICES)


              IMMUNOGEN, INC. 2001 NON-EMPLOYEE DIRECTOR STOCK PLAN
              -----------------------------------------------------
                            (FULL TITLE OF THE PLAN)


                                 Mitchel Sayare
                            Chairman of the Board and
                             Chief Executive Officer
                                 ImmunoGen, Inc.
                                128 Sidney Street
                         Cambridge, Massachusetts 02139
                         ------------------------------
                     (NAME AND ADDRESS OF AGENT FOR SERVICE)


                                 (617) 995-2500
                                 --------------
          (TELEPHONE NUMBER, INCLUDING AREA CODE, OF AGENT FOR SERVICE)


                  Please send copies of all communications to:

                            Jonathan L. Kravetz, Esq.
                           Mintz, Levin, Cohn, Ferris,
                             Glovsky and Popeo, P.C.
                              One Financial Center
                                Boston, MA 02111
                                 (617) 542-6000



                                        1

<PAGE>


                         CALCULATION OF REGISTRATION FEE

<TABLE>
<CAPTION>

                                         Proposed          Proposed
Title of                                 maximum           maximum
securities         Amount                offering          aggregate       Amount of
to be              to be                 price per         offering        registration
registered         registered(1)         unit(2)           price(2)        fee
<S>                <C>                   <C>               <C>               <C>
Common Stock,
$.01 par value      50,000                $16.10            $805,000          $192.40
                    ======                ======            ========          =======
</TABLE>


(1)      The number of shares of common stock, par value $.01 per share (the
         "Common Stock"), consists of the aggregate number of shares which may
         hereafter be granted under the ImmunoGen, Inc. 2001 Non-Employee
         Director Stock Plan (the "2001 Plan"). The maximum number of shares
         which may be granted under the 2001 Plan is subject to adjustment in
         accordance with certain anti-dilution and other provisions of the
         2001 Plan. Accordingly, pursuant to Rule 416 under the Securities Act
         of 1933, as amended (the "Securities Act"), this Registration
         Statement covers, in addition to the number of shares stated above,
         an indeterminable number of shares which may be subject to grant or
         otherwise issuable after the operation of any such anti-dilution and
         other provisions.

(2)      This calculation is made solely for the purpose of determining the
         registration fee pursuant to the provisions of Rules 457(c) and 457(h)
         under the Securities Act of 1933, as amended and based upon the average
         of the high and low sales prices per share of the Common Stock as
         reported on the Nasdaq National Market System on December 14, 2001.


EXPLANATORY NOTE

         This Registration Statement relates to the registration of 50,000
shares of Common Stock authorized for issuance under the 2001 Plan. In
accordance with the instructional Note to Part I of Form S-8 as promulgated by
the Securities and Exchange Commission, the information specified by Part I of
Form S-8 has been omitted from this Registration Statement on Form S-8 for
offers of Common Stock pursuant to the 2001 Plan.

                                     PART II
               INFORMATION REQUIRED IN THE REGISTRATION STATEMENT

ITEM 3. INCORPORATION OF DOCUMENTS BY REFERENCE.

         The following documents filed by the Registrant with the Securities and
Exchange Commission (the "Commission") are incorporated herein by reference:

         (a)      The Registrant's annual report on Form 10-K (Commission File
                  No. 0-17999) for the fiscal year ended June 30, 2001.

         (b)      The Registrant's quarterly report on Form 10-Q (Commission
                  File No. 0-17999) for the quarter ended September 30, 2001.

         (c)      The Registrant's current reports on Form 8-K filed with the
                  Commission on September 7, 2001 and November 29, 2001 and on
                  Form 8-K/A filed with the Commission on October 5, 2001.

         (d)      The description of the Common Stock included in the
                  Registrant's Registration Statement on Form 8-A under the
                  Securities Exchange Act of 1934 (File No. 0-17999), filed with
                  the Commission on September 22, 1989, including any amendment
                  or report filed for the purpose of updating such description.


                                       2
<PAGE>


         (e)      The Registrant's proxy materials on Schedule 14A filed with
                  the Commission on October 4, 2001.

         All reports and other documents subsequently filed by the Registrant
with the Commission pursuant to Sections 13(a), 13(c), 14 and 15(d) of the
Exchange Act prior to the filing of a post-effective amendment which indicates
that all securities covered by this Registration Statement have been sold or
which deregisters all such securities then remaining unsold shall be deemed to
be incorporated by reference herein and to be a part hereof from the date of the
filing of such reports and documents.

ITEM 4.  DESCRIPTION OF SECURITIES.

         Not applicable.

ITEM 5.  INTERESTS OF NAMED EXPERTS AND COUNSEL.

         Not applicable.

ITEM 6.  INDEMNIFICATION OF DIRECTORS AND OFFICERS.

         Incorporated herein by reference from the Registrant's Registration
Statement on Form S-3 (Registration No. 333-57234), as amended.

ITEM 7.  EXEMPTION FROM REGISTRATION CLAIMED.

         Not applicable.

ITEM 8.  EXHIBITS.

EXHIBIT NO.   DESCRIPTION

(4.1)         Form of Common Stock Certificate (previously filed as Exhibit 4.2
              to the Registrant's Registration Statement on Form S-1,
              Registration No. 33-31219, as amended, and incorporated herein by
              reference)

(4.2)         Restated Articles of Organization of the Registrant (previously
              filed as Exhibit 3.1 to the Registrant's Registration Statement on
              Form S-1, Registration No. 33-38883, as amended, and incorporated
              herein by reference)

(4.3)         Amendment to Articles of Organization of Registrant

(4.4)         By-Laws, as amended, of the Registrant (previously filed as
              Exhibit 3.2 to the Registrant's annual report on Form 10-K for the
              fiscal year ended June 30, 1990, and incorporated herein by
              reference)

(5.1)         Opinion of Mintz, Levin, Cohn, Ferris, Glovsky and Popeo, P.C.,
              with respect to the legality of the shares being registered

(23.1)        Consent of Mintz, Levin, Cohn, Ferris, Glovsky and Popeo, P.C.
              (included in opinion of counsel filed as Exhibit 5.1)

(23.2)        Consent of PricewaterhouseCoopers LLP

(24)          Power of Attorney to file future amendments (included on the
              signature page of this Registration Statement)

(99)          ImmunoGen, Inc. 2001 Non-Employee Director Stock Plan


                                       3
<PAGE>


ITEM 9. UNDERTAKINGS.

         (a)      The undersigned Registrant hereby undertakes:

                  (1) to file, during any period in which offers or sales are
         being made, a post-effective amendment to this Registration Statement:
         (i) to include any prospectus required by Section 10(a)(3) of the
         Securities Act of 1933; (ii) to reflect in the prospectus any facts or
         events arising after the effective date of the Registration Statement
         (or the most recent post-effective amendment thereof) which,
         individually or in the aggregate, represent a fundamental change in the
         information set forth in the Registration Statement; (iii) to include
         any material information with respect to the plan of distribution not
         previously disclosed in the Registration Statement or any material
         change to such information in the Registration Statement;
         notwithstanding the foregoing, any increase or decrease in volume of
         securities offered (if the total dollar value of securities offered
         would not exceed that which was registered) and any deviation from the
         low or high end of the estimated maximum offering range may be
         reflected in the form of prospectus filed with the Commission pursuant
         to Rule 424(b) of Regulation C under the Securities Act of 1933, as
         amended, if, in the aggregate, the changes in volume and price
         represent no more than a 20% change in the maximum aggregate offering
         price set forth in the "Calculation of Registration Fee" table in the
         effective Registration Statement; provided, however, that paragraphs
         (a)(1)(i) and (ii) shall not apply if the information required to be
         included in a post-effective amendment by those paragraphs is contained
         in periodic reports filed by the registrant pursuant to Section 13 or
         Section 15(d) of the Securities Exchange Act of 1934 that are
         incorporated by reference in the registration statement.

                  (2) that, for the purpose of determining any liability under
         the Securities Act of 1933, each such post-effective amendment shall be
         deemed to be a new registration statement relating to the securities
         offered therein, and the offering of such securities at that time shall
         be deemed to be the initial bona fide offering thereof.

                  (3) to remove from registration by means of a post-effective
         amendment any of the securities being registered which remain unsold at
         the termination of the offering.

         (b) The undersigned Registrant hereby undertakes that, for purposes of
determining any liability under the Securities Act of 1933, each filing of the
Registrant's annual report pursuant to Section 13(a) or Section 15(d) of the
Securities Exchange Act of 1934 that is incorporated by reference in this
Registration Statement shall be deemed to be a new registration statement
relating to the securities offered therein, and the offering of such securities
at that time shall be deemed to be the initial bona fide offering thereof.

         (c) Insofar as indemnification for liabilities arising under the
Securities Act of 1933 may be permitted to directors, officers and controlling
persons of the Registrant pursuant to the foregoing provisions, or otherwise,
the Registrant has been advised that in the opinion of the Securities and
Exchange Commission such indemnification is against public policy as expressed
in the Securities Act of 1933 and is, therefore, unenforceable. In the event
that a claim for indemnification against such liabilities (other than the
payment by the Registrant of expenses incurred or paid by a director, officer or
controlling person of the Registrant in the successful defense of any action,
suit or proceeding) is asserted by such director, officer or controlling person
in connection with the securities being registered, the Registrant will, unless
in the opinion of its counsel the matter has been settled by controlling
precedent, submit to a court of appropriate jurisdiction the question whether
such indemnification by it is against public policy as expressed in the
Securities Act of 1933 and will be governed by the final adjudication of such
issue.


                                       4
<PAGE>


                                   SIGNATURES

         Pursuant to the requirements of the Securities Act of 1933, the
Registrant certifies that it has reasonable grounds to believe that it meets all
of the requirements for filing on Form S-8 and has duly caused this Registration
Statement to be signed on its behalf by the undersigned, thereunto duly
authorized, in the City of Cambridge, Commonwealth of Massachusetts, on December
17, 2001.

                                               IMMUNOGEN, INC.

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

         We, the undersigned officers and directors of ImmunoGen, Inc., hereby
severally constitute and appoint Mitchel Sayare and Walter Blattler and each of
them singly, as true and lawful attorneys, with full power to them and each of
them singly, to sign for us in our names in the capacities indicated below, all
additional amendments to this registration statement, and generally to do all
things in our names and on our behalf in such capacities to enable ImmunoGen,
Inc. to comply with the provisions of the Securities Act of 1933, as amended,
and all applicable requirements of the Securities and Exchange Commission.

         Pursuant to the requirements of the Securities Act of 1933, this
Registration Statement has been signed by the following persons in the
capacities and on the dates indicated.

<TABLE>
<CAPTION>

Title:                                                                 Date:
<S>                        <C>                                         <C>
/s/ Mitchel Sayare         Chairman of the Board                       December 17, 2001
-----------------------    of Directors and
  Mitchel Sayare           Chief Executive Officer
                           principal executive officer)


/s/ Gregg D. Beloff        Vice President and Chief                    December 17, 2001
-----------------------    Financial Officer
  Gregg D. Beloff          (principal accounting officer)


/s/ Walter A. Blattler     Executive Vice President,                   December 17, 2001
-----------------------    Science and Technology,
  Walter A. Blattler       and Director


/s/ David W. Carter        Director                                    December 17, 2001
-----------------------
  David W. Carter


/s/ Michael R. Eisenson    Director                                    December 17, 2001
-----------------------
  Michael R. Eisenson


/s/ Stuart F. Feiner       Director                                    December 17, 2001
----------------------
  Stuart F. Feiner


/s/ Mark B. Skaletsky      Director                                    December 17, 2001
----------------------
  Mark B. Skaletsky
</TABLE>


                                       5
<PAGE>


                                 IMMUNOGEN, INC.

                                  EXHIBIT INDEX


EXHIBIT NO.   DESCRIPTION

(4.1)         Form of Common Stock Certificate (previously filed as Exhibit 4.2
              to the Registrant's Registration Statement on Form S-1,
              Registration No. 33-31219, as amended, and incorporated herein by
              reference)

(4.2)         Restated Articles of Organization of the Registrant (previously
              filed as Exhibit 3.1 to the Registrant's Registration Statement on
              Form S-1, Registration No. 33-38883, as amended, and incorporated
              herein by reference)

(4.3)         Amendment to Articles of Organization of Registrant

(4.4)         By-Laws, as amended, of the Registrant (previously filed as
              Exhibit 3.2 to the Registrant's annual report on Form 10-K for the
              fiscal year ended June 30, 1990, and incorporated herein by
              reference)

(5.1)         Opinion of Mintz, Levin, Cohn, Ferris, Glovsky and Popeo, P.C.,
              with respect to the legality of the shares being registered

(23.1)        Consent of Mintz, Levin, Cohn, Ferris, Glovsky and Popeo, P.C.
              (included in opinion of counsel filed as Exhibit 5.1)

(23.2)        Consent of PricewaterhouseCoopers LLP

(24)          Power of Attorney to file future amendments (included on the
              signature page of this Registration Statement)

(99)          ImmunoGen, Inc. 2001 Non-Employee Director Stock Option Plan


                                       6
[{"type": "S-8", "sequence": "1", "filename": "a2066251zs-8.txt", "description": "S-8", "secsgml_size_bytes": 17769}]
{"company-data": {"conformed-name": "IMMUNOGEN INC", "cik": "0000855654", "assigned-sic": "2834", "irs-number": "042726691", "state-of-incorporation": "MA", "fiscal-year-end": "0630"}, "filing-values": {"form-type": "S-8", "act": "33", "file-number": "333-75374", "film-number": "1816816"}, "business-address": {"street1": "128 SIDNEY ST", "city": "CAMBRIDGE", "state": "MA", "zip": "02139", "phone": "6176619312"}, "mail-address": {"street1": "128 SIDENEY ST", "city": "CAMBRIDGE", "state": "MA", "zip": "02139"}}
As filed with the Securities and Exchange Commission
                              On December 18, 2001

                              Registration No. 33-

                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549

                                    FORM S-8
                             REGISTRATION STATEMENT

                                      UNDER

                           THE SECURITIES ACT OF 1933

                                 IMMUNOGEN, INC.
                                 ---------------
             (EXACT NAME OF REGISTRANT AS SPECIFIED IN ITS CHARTER)

        MASSACHUSETTS                                         04-2726691
        ----------------------------------------------------------------
(STATE OR OTHER JURISDICTION OF                            (I.R.S. EMPLOYER
INCORPORATION OR ORGANIZATION)                            IDENTIFICATION NO.)

                128 SIDNEY STREET, CAMBRIDGE, MASSACHUSETTS 02139
                -------------------------------------------------
                    (ADDRESS OF PRINCIPAL EXECUTIVE OFFICES)

              IMMUNOGEN, INC. 2001 NON-EMPLOYEE DIRECTOR STOCK PLAN
              -----------------------------------------------------
                            (FULL TITLE OF THE PLAN)

                                 Mitchel Sayare
                            Chairman of the Board and
                             Chief Executive Officer
                                 ImmunoGen, Inc.
                                128 Sidney Street
                         Cambridge, Massachusetts 02139
                         ------------------------------
                     (NAME AND ADDRESS OF AGENT FOR SERVICE)

                                 (617) 995-2500
                                 --------------
          (TELEPHONE NUMBER, INCLUDING AREA CODE, OF AGENT FOR SERVICE)

                  Please send copies of all communications to:

                            Jonathan L. Kravetz, Esq.
                           Mintz, Levin, Cohn, Ferris,
                             Glovsky and Popeo, P.C.
                              One Financial Center
                                Boston, MA 02111
                                 (617) 542-6000

                                        1
CALCULATION OF REGISTRATION FEE
Proposed          Proposed
Title of                                 maximum           maximum
securities         Amount                offering          aggregate       Amount of
to be              to be                 price per         offering        registration
registered         registered(1)         unit(2)           price(2)        fee
Common Stock,
$.01 par value      50,000                $16.10            $805,000          $192.40
                    ======                ======            ========          =======
(1)      The number of shares of common stock, par value $.01 per share (the
         "Common Stock"), consists of the aggregate number of shares which may
         hereafter be granted under the ImmunoGen, Inc. 2001 Non-Employee
         Director Stock Plan (the "2001 Plan"). The maximum number of shares
         which may be granted under the 2001 Plan is subject to adjustment in
         accordance with certain anti-dilution and other provisions of the
         2001 Plan. Accordingly, pursuant to Rule 416 under the Securities Act
         of 1933, as amended (the "Securities Act"), this Registration
         Statement covers, in addition to the number of shares stated above,
         an indeterminable number of shares which may be subject to grant or
         otherwise issuable after the operation of any such anti-dilution and
         other provisions.

(2)      This calculation is made solely for the purpose of determining the
         registration fee pursuant to the provisions of Rules 457(c) and 457(h)
         under the Securities Act of 1933, as amended and based upon the average
         of the high and low sales prices per share of the Common Stock as
         reported on the Nasdaq National Market System on December 14, 2001.

EXPLANATORY NOTE

         This Registration Statement relates to the registration of 50,000
shares of Common Stock authorized for issuance under the 2001 Plan. In
accordance with the instructional Note to Part I of Form S-8 as promulgated by
the Securities and Exchange Commission, the information specified by Part I of
Form S-8 has been omitted from this Registration Statement on Form S-8 for
offers of Common Stock pursuant to the 2001 Plan.

                                     PART II
               INFORMATION REQUIRED IN THE REGISTRATION STATEMENT

ITEM 3. INCORPORATION OF DOCUMENTS BY REFERENCE.

         The following documents filed by the Registrant with the Securities and
Exchange Commission (the "Commission") are incorporated herein by reference:

         (a)      The Registrant's annual report on Form 10-K (Commission File
                  No. 0-17999) for the fiscal year ended June 30, 2001.

         (b)      The Registrant's quarterly report on Form 10-Q (Commission
                  File No. 0-17999) for the quarter ended September 30, 2001.

         (c)      The Registrant's current reports on Form 8-K filed with the
                  Commission on September 7, 2001 and November 29, 2001 and on
                  Form 8-K/A filed with the Commission on October 5, 2001.

         (d)      The description of the Common Stock included in the
                  Registrant's Registration Statement on Form 8-A under the
                  Securities Exchange Act of 1934 (File No. 0-17999), filed with
                  the Commission on September 22, 1989, including any amendment
                  or report filed for the purpose of updating such description.

                                       2
(e)      The Registrant's proxy materials on Schedule 14A filed with
                  the Commission on October 4, 2001.

         All reports and other documents subsequently filed by the Registrant
with the Commission pursuant to Sections 13(a), 13(c), 14 and 15(d) of the
Exchange Act prior to the filing of a post-effective amendment which indicates
that all securities covered by this Registration Statement have been sold or
which deregisters all such securities then remaining unsold shall be deemed to
be incorporated by reference herein and to be a part hereof from the date of the
filing of such reports and documents.

ITEM 4.  DESCRIPTION OF SECURITIES.

         Not applicable.

ITEM 5.  INTERESTS OF NAMED EXPERTS AND COUNSEL.

         Not applicable.

ITEM 6.  INDEMNIFICATION OF DIRECTORS AND OFFICERS.

         Incorporated herein by reference from the Registrant's Registration
Statement on Form S-3 (Registration No. 333-57234), as amended.

ITEM 7.  EXEMPTION FROM REGISTRATION CLAIMED.

         Not applicable.

ITEM 8.  EXHIBITS.

EXHIBIT NO.   DESCRIPTION

(4.1)         Form of Common Stock Certificate (previously filed as Exhibit 4.2
              to the Registrant's Registration Statement on Form S-1,
              Registration No. 33-31219, as amended, and incorporated herein by
              reference)

(4.2)         Restated Articles of Organization of the Registrant (previously
              filed as Exhibit 3.1 to the Registrant's Registration Statement on
              Form S-1, Registration No. 33-38883, as amended, and incorporated
              herein by reference)

(4.3)         Amendment to Articles of Organization of Registrant

(4.4)         By-Laws, as amended, of the Registrant (previously filed as
              Exhibit 3.2 to the Registrant's annual report on Form 10-K for the
              fiscal year ended June 30, 1990, and incorporated herein by
              reference)

(5.1)         Opinion of Mintz, Levin, Cohn, Ferris, Glovsky and Popeo, P.C.,
              with respect to the legality of the shares being registered

(23.1)        Consent of Mintz, Levin, Cohn, Ferris, Glovsky and Popeo, P.C.
              (included in opinion of counsel filed as Exhibit 5.1)

(23.2)        Consent of PricewaterhouseCoopers LLP

(24)          Power of Attorney to file future amendments (included on the
              signature page of this Registration Statement)

(99)          ImmunoGen, Inc. 2001 Non-Employee Director Stock Plan

                                       3
ITEM 9. UNDERTAKINGS.

         (a)      The undersigned Registrant hereby undertakes:

                  (1) to file, during any period in which offers or sales are
         being made, a post-effective amendment to this Registration Statement:
         (i) to include any prospectus required by Section 10(a)(3) of the
         Securities Act of 1933; (ii) to reflect in the prospectus any facts or
         events arising after the effective date of the Registration Statement
         (or the most recent post-effective amendment thereof) which,
         individually or in the aggregate, represent a fundamental change in the
         information set forth in the Registration Statement; (iii) to include
         any material information with respect to the plan of distribution not
         previously disclosed in the Registration Statement or any material
         change to such information in the Registration Statement;
         notwithstanding the foregoing, any increase or decrease in volume of
         securities offered (if the total dollar value of securities offered
         would not exceed that which was registered) and any deviation from the
         low or high end of the estimated maximum offering range may be
         reflected in the form of prospectus filed with the Commission pursuant
         to Rule 424(b) of Regulation C under the Securities Act of 1933, as
         amended, if, in the aggregate, the changes in volume and price
         represent no more than a 20% change in the maximum aggregate offering
         price set forth in the "Calculation of Registration Fee" table in the
         effective Registration Statement; provided, however, that paragraphs
         (a)(1)(i) and (ii) shall not apply if the information required to be
         included in a post-effective amendment by those paragraphs is contained
         in periodic reports filed by the registrant pursuant to Section 13 or
         Section 15(d) of the Securities Exchange Act of 1934 that are
         incorporated by reference in the registration statement.

                  (2) that, for the purpose of determining any liability under
         the Securities Act of 1933, each such post-effective amendment shall be
         deemed to be a new registration statement relating to the securities
         offered therein, and the offering of such securities at that time shall
         be deemed to be the initial bona fide offering thereof.

                  (3) to remove from registration by means of a post-effective
         amendment any of the securities being registered which remain unsold at
         the termination of the offering.

         (b) The undersigned Registrant hereby undertakes that, for purposes of
determining any liability under the Securities Act of 1933, each filing of the
Registrant's annual report pursuant to Section 13(a) or Section 15(d) of the
Securities Exchange Act of 1934 that is incorporated by reference in this
Registration Statement shall be deemed to be a new registration statement
relating to the securities offered therein, and the offering of such securities
at that time shall be deemed to be the initial bona fide offering thereof.

         (c) Insofar as indemnification for liabilities arising under the
Securities Act of 1933 may be permitted to directors, officers and controlling
persons of the Registrant pursuant to the foregoing provisions, or otherwise,
the Registrant has been advised that in the opinion of the Securities and
Exchange Commission such indemnification is against public policy as expressed
in the Securities Act of 1933 and is, therefore, unenforceable. In the event
that a claim for indemnification against such liabilities (other than the
payment by the Registrant of expenses incurred or paid by a director, officer or
controlling person of the Registrant in the successful defense of any action,
suit or proceeding) is asserted by such director, officer or controlling person
in connection with the securities being registered, the Registrant will, unless
in the opinion of its counsel the matter has been settled by controlling
precedent, submit to a court of appropriate jurisdiction the question whether
such indemnification by it is against public policy as expressed in the
Securities Act of 1933 and will be governed by the final adjudication of such
issue.

                                       4
SIGNATURES

         Pursuant to the requirements of the Securities Act of 1933, the
Registrant certifies that it has reasonable grounds to believe that it meets all
of the requirements for filing on Form S-8 and has duly caused this Registration
Statement to be signed on its behalf by the undersigned, thereunto duly
authorized, in the City of Cambridge, Commonwealth of Massachusetts, on December
17, 2001.

                                               IMMUNOGEN, INC.

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

         We, the undersigned officers and directors of ImmunoGen, Inc., hereby
severally constitute and appoint Mitchel Sayare and Walter Blattler and each of
them singly, as true and lawful attorneys, with full power to them and each of
them singly, to sign for us in our names in the capacities indicated below, all
additional amendments to this registration statement, and generally to do all
things in our names and on our behalf in such capacities to enable ImmunoGen,
Inc. to comply with the provisions of the Securities Act of 1933, as amended,
and all applicable requirements of the Securities and Exchange Commission.

         Pursuant to the requirements of the Securities Act of 1933, this
Registration Statement has been signed by the following persons in the
capacities and on the dates indicated.
Title:                                                                 Date:
/s/ Mitchel Sayare         Chairman of the Board                       December 17, 2001
-----------------------    of Directors and
  Mitchel Sayare           Chief Executive Officer
                           principal executive officer)

/s/ Gregg D. Beloff        Vice President and Chief                    December 17, 2001
-----------------------    Financial Officer
  Gregg D. Beloff          (principal accounting officer)

/s/ Walter A. Blattler     Executive Vice President,                   December 17, 2001
-----------------------    Science and Technology,
  Walter A. Blattler       and Director

/s/ David W. Carter        Director                                    December 17, 2001
-----------------------
  David W. Carter

/s/ Michael R. Eisenson    Director                                    December 17, 2001
-----------------------
  Michael R. Eisenson

/s/ Stuart F. Feiner       Director                                    December 17, 2001
----------------------
  Stuart F. Feiner

/s/ Mark B. Skaletsky      Director                                    December 17, 2001
----------------------
  Mark B. Skaletsky
5
IMMUNOGEN, INC.

                                  EXHIBIT INDEX

EXHIBIT NO.   DESCRIPTION

(4.1)         Form of Common Stock Certificate (previously filed as Exhibit 4.2
              to the Registrant's Registration Statement on Form S-1,
              Registration No. 33-31219, as amended, and incorporated herein by
              reference)

(4.2)         Restated Articles of Organization of the Registrant (previously
              filed as Exhibit 3.1 to the Registrant's Registration Statement on
              Form S-1, Registration No. 33-38883, as amended, and incorporated
              herein by reference)

(4.3)         Amendment to Articles of Organization of Registrant

(4.4)         By-Laws, as amended, of the Registrant (previously filed as
              Exhibit 3.2 to the Registrant's annual report on Form 10-K for the
              fiscal year ended June 30, 1990, and incorporated herein by
              reference)

(5.1)         Opinion of Mintz, Levin, Cohn, Ferris, Glovsky and Popeo, P.C.,
              with respect to the legality of the shares being registered

(23.1)        Consent of Mintz, Levin, Cohn, Ferris, Glovsky and Popeo, P.C.
              (included in opinion of counsel filed as Exhibit 5.1)

(23.2)        Consent of PricewaterhouseCoopers LLP

(24)          Power of Attorney to file future amendments (included on the
              signature page of this Registration Statement)

(99)          ImmunoGen, Inc. 2001 Non-Employee Director Stock Option Plan

                                       6