Exhibit 99


                                 IMMUNOGEN, INC.

                      2001 NON-EMPLOYEE DIRECTOR STOCK PLAN

1.       DEFINITIONS.

         Unless otherwise specified or unless the context otherwise requires,
         the following terms, as used in this ImmunoGen, Inc. 2001 Non-Employee
         Director Stock Plan, have the following meanings:

                  ADMINISTRATOR means the Board of Directors, unless it has
                  delegated power to act on its behalf to the Committee, in
                  which case the Administrator means the Committee.

                  AFFILIATE means a corporation which, for purposes of Section
                  424 of the Code, is a parent or subsidiary of the Company,
                  direct or indirect.

                  ANNUAL AWARD means a grant under the Plan representing the
                  annual retainer payable to any Participant for serving on the
                  Board of Directors, payable in (i) Stock or (ii) Stock units,
                  based upon a Participant's election.

                  AWARD means an Annual Award or Meeting Award, or both, as the
                  context requires.

                  AWARD AGREEMENT means an agreement between the Company and a
                  Participant for the issuance of Stock Rights delivered
                  pursuant to the Plan, in such form as approved by the
                  Administrator, which shall contain such terms and conditions
                  as the Administrator determines to be appropriate and in the
                  best interest of the Company.

                  BOARD OF DIRECTORS means the Board of Directors of the
                  Company.

                  CODE means the United States Internal Revenue Code of 1986, as
                  amended.

                  COMMITTEE means the committee of the Board of Directors to
                  which the Board of Directors has delegated power to act under
                  or pursuant to the provisions of the Plan.



                  COMMON STOCK means shares of the Company's common stock, $.01
                  par value per share.

                  COMPANY means ImmunoGen, Inc., a Massachusetts corporation.

                  ELECTION FORM means the form on which a Participant elects the
                  form of Award he or she will receive pursuant to Section 6
                  hereof.

                  FAIR MARKET VALUE of a share of Common Stock means:

                  (1) If the Common Stock is listed on a national securities
                  exchange or traded in the over-the-counter market and sales
                  prices are regularly reported for the Common Stock, the
                  closing or last price of the Common Stock on the Composite
                  Tape or other comparable reporting system for the trading day
                  on the date of the grant of the Stock Right;

                  (2) If the Common Stock is not traded on a national securities
                  exchange but is traded on the over-the-counter market, if
                  sales prices are not regularly reported for the Common Stock
                  for the trading day referred to in clause (1), and if bid and
                  asked prices for the Common Stock are regularly reported, the
                  mean between the bid and the asked price for the Common Stock
                  at the close of trading in the over-the-counter market for the
                  trading day on which Common Stock was traded on the date of
                  the grant of the Stock Right; and

                  (3) If the Common Stock is neither listed on a national
                  securities exchange nor traded in the over-the-counter market,
                  such value as the Administrator, in good faith, shall
                  determine.

                  MEETING AWARD means a grant under the Plan representing the
                  meeting and committee attendance and chairperson fees payable
                  to any Participant for serving on the Board of Directors,
                  payable in (i) cash, (ii) Stock or (iii) Stock Units, based
                  upon a Participant's election.

                  NON-EMPLOYEE DIRECTOR means each member of the Board of
                  Directors who is not an employee of the Company or of any
                  Affiliate.

                  PARTICIPANT means a Non-Employee Director to whom one or more
                  Stock Rights are granted under the Plan. As used herein,
                  "Participant" shall include "Participant's Survivors" where
                  the context requires.

                  PLAN means this ImmunoGen, Inc. 2001 Non-Employee Director
                  Stock Plan.

                  STOCK means shares of the Common Stock which have been or
                  may be granted under the Plan or any shares of capital
                  stock into which the Stock are changed or for which they are
                  exchanged within the provisions of Section 3 of the Plan.
                  Stock issued under the Plan may be authorized and unissued
                  Stock or Stock held by the Company in its treasury, or both.


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                  STOCK RIGHT means a right to Stock or Stock Units of the
                  Company granted pursuant to the Plan, in the form of an
                  Award.

                  STOCK UNIT means a unit, equivalent in value to a share of
                  Common Stock, credited by means of a bookkeeping entry in the
                  books of the Company to a Participant's account pursuant to
                  the terms and conditions of the Plan.

                  SURVIVORS means a deceased Participant's legal representatives
                  and/or any person or persons who acquired the Participant's
                  rights to a Stock Right by will or by the laws of descent and
                  distribution.

                  TERMINATION DATE means the date upon which a Participant
                  ceases to be a member of the Board of Directors for any reason
                  whatsoever, including death or disability.

2.       PURPOSES OF THE PLAN.

         The purpose of the Plan is to provide a means by which the Company can
compensate Non-Employee Directors for their service on the Board of Directors
and to encourage continued ownership of Stock by the Non-Employee Directors, in
order to attract such people to serve on the Board of Directors and to induce
them to work for the benefit of the Company. The Plan provides for (i) the
granting of Awards to Non-Employee Directors and (ii) subject to Section 6
hereof, the election by Non-Employee Directors to have all or a portion of their
Awards credited in the form of Stock Units.

3.       STOCK SUBJECT TO THE PLAN.

         The number of shares of Stock which may be the subject of Stock Rights
granted pursuant to this Plan shall be 50,000, or the equivalent of such number
of shares of Stock after the Administrator, in its sole discretion, has
interpreted the effect of any stock split, stock dividend, combination,
recapitalization or similar transaction in accordance with Section 17 of the
Plan. Upon payment in cash of the benefit provided by any Award granted under
the Plan, any Stock Units that were covered by that Award shall again be
available for the granting of Stock Units under the Plan.

4.       ADMINISTRATION OF THE PLAN.

         Subject to the provisions of the Plan, the Administrator is authorized
to:

         a.  Interpret the provisions of the Plan or of any Award Agreement and
             to make all rules and determinations which it deems necessary or
             advisable for the administration of the Plan;

         b.  Determine which Non-Employee Directors shall be granted Awards;
             and


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         c.  Determine the number of shares of Stock for which a Stock Right or
             Stock Rights shall be granted.

Subject to the foregoing, the interpretation and construction by the
Administrator of any provisions of the Plan or of any Stock Right granted under
it shall be final, unless otherwise determined by the Board of Directors, if the
Administrator is the Committee.

5.       ELIGIBILITY FOR PARTICIPATION.

         The Administrator will, in its sole discretion, name the
Participants in the Plan, provided, however, that each Participant must be a
Non-Employee Director at the time an Award is granted. Notwithstanding the
foregoing, the Administrator may authorize the grant of an Award to a person
not then a Non-Employee Director; provided, however, that the actual grant of
such Award shall be conditioned upon such person becoming eligible to become
a Participant at or prior to the time of the delivery of the Award Agreement
evidencing such Award. The granting of any Award to any individual shall
neither entitle that individual to, nor disqualify him or her from,
participation in any other grant of Awards.

6.       CERTAIN ELECTIONS.

         Each Participant shall, subject to the terms of this Section, have
the right to elect to receive all or a portion of (i) an Annual Award in the
form of Stock or Stock Units and (ii) a Meeting Award in the form of cash,
Stock or Stock Units, by completing, signing and delivering to the Treasurer
of the Company an Election Form for each calendar year while this Plan is in
effect, starting in January 2002, by December 31 of the immediately preceding
year, provided that (1) any such election shall apply only to Awards made
after the date on which such election is made and (2) any person who becomes
a Non-Employee Director during the course of a calendar year shall have the
right to make his or her election in respect of Awards earned after the date
he or she becomes a Non-Employee Director by completing an Election Form
within 30 days after first becoming a Non-Employee Director. A Participant
shall elect to receive an Annual Award entirely in Stock or Stock Units but
not in a combination thereof, and shall elect to receive annually all Meeting
Awards entirely in cash, Stock or Stock Units but not in a combination
thereof.

         Any election made pursuant to the terms of this Plan shall remain
effective until it is changed by the completion, signature, and delivery to the
Treasurer of the Company of a new Election Form in accordance with the terms of
the Plan, which shall take effect for the calendar year(s) or other applicable
period commencing after the delivery of the Election Form.

         If no election is made, and no prior election remains effective, the
Participant shall be deemed to have elected to receive all Annual Awards in the
form of Stock and all Meeting Awards in the form of cash.


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7.       NUMBER OF STOCK RIGHTS TO BE ISSUED.

         During a calendar year, the number of Stock Rights to be received by
a Participant by the issuance of stock or credited in the books of the
Company to the account of a Participant for Stock Units shall be such number
of Stock Rights (including fractional Stock Rights calculated to four decimal
points rounded down) as is obtained on a quarterly basis by dividing the
total dollar amount that the Participant has elected to be paid in Stock
Rights under the Plan by the Fair Market Value on the last date of the
Company's fiscal quarter in which the Awards for each calendar quarter are
made.

         No fractional shares shall be issued under the Plan and the person
exercising a Stock Right shall receive from the Company cash in lieu of such
fractional shares equal to the Fair Market Value thereof.

8.       CREDIT FOR DIVIDENDS ON STOCK UNITS.

         A Participant's account covering Stock Units shall be credited with
dividend equivalents in the form of additional Stock Units when cash dividends
are paid on the Common Stock. Such dividend equivalents shall be computed by
dividing: (a) the amount obtained by multiplying the amount of the dividend
declared and paid per share by the number of Stock Units recorded in the
Participant's account on the record date for the payment of such dividend, by
(b) the Fair Market Value on the dividend payment date for such dividend, with
fractions computed to four decimal places (rounded down).

9.       REPORTING OF STOCK UNITS.

         Statements of Stock Unit accounts will be provided to the Participants
on a quarterly basis.


10.      TERMS AND CONDITIONS OF STOCK RIGHTS.

         Each Stock Right granted to a Participant shall state the date prior
to which the Stock Right must be accepted by the Participant, and the
principal terms of each Stock Right shall be set forth in an Award Agreement,
duly executed by the Company and, to the extent required by law or requested
by the Company, by the Participant. Such Award Agreement shall state the
number of shares of Stock Rights to which the Award pertains.


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11.      ACCEPTANCE OF STOCK RIGHT AND ISSUE OF STOCK.

         A Stock Right (or any part or installment thereof) shall be accepted
by executing the Award Agreement and delivering it to the Company at its
principal office address, upon compliance with any other conditions set forth
in the Award Agreement.

         The Company shall then reasonably promptly deliver the Stock or
credit the number of Stock Units as to which such Award was accepted to the
Participant (or to the Participant's Survivors, as the case may be), subject
to any escrow provision set forth in the Award Agreement. In determining what
constitutes "reasonably promptly," it is expressly understood that the
issuance and delivery of the Stock or Stock Units may be delayed by the
Company in order to comply with any law or regulation (including, without
limitation, state securities or "blue sky" laws) which requires the Company
to take any action with respect to the Stock or Stock Units prior to their
issuance.

         The Administrator may, in its discretion, amend any term or condition
of an outstanding Award or Award Agreement provided (i) such term or condition
as amended is permitted by the Plan, and (ii) any such amendment shall be made
only with the consent of the Participant to whom the Award was made, if the
amendment is adverse to the Participant.

12.      RIGHTS AS A SHAREHOLDER.

         No Participant to whom a Stock Right has been granted shall have rights
as a shareholder with respect to any Stock covered by such Stock Right, except
after acceptance of the Award for the Stock and registration of the Stock in the
Company's stock register in the name of the Participant.

13.      ASSIGNABILITY AND TRANSFERABILITY OF STOCK RIGHTS.

         By its terms, a Stock Right granted to a Participant shall not be
transferable by the Participant other than (i) by will or by the laws of descent
and distribution, or (ii) as otherwise determined by the Administrator and set
forth in any applicable Award Agreement. The designation of a beneficiary of a
Stock Right by a Participant, with the prior approval of the Administrator and
in such form as the Administrator shall prescribe, shall not be deemed a
transfer prohibited by this Section. Except as provided above, a Stock Right
shall only be exercisable or may only be accepted, during the Participant's
lifetime, by such Participant (or by his or her legal representative) and shall
not be assigned, pledged or hypothecated in any way (whether by operation of law
or otherwise) and shall not be subject to execution, attachment or similar
process. Any attempted transfer, assignment, pledge, hypothecation or other
disposition of any Stock Right or of any rights granted thereunder contrary to
the provisions of this Plan, or the levy of any attachment or similar process
upon a Stock Right, shall be null and void.


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14.      EFFECT OF TERMINATION OF DIRECTORSHIP ON STOCK UNITS.

         In the event of a termination of service as a Non-Employee Director of
the Company for any reason, a Participant shall receive, not later than thirty
days following the Participant's Termination Date, a lump sum payment in cash
equal to the number of Stock Units recorded in the Participant's account on the
Termination Date multiplied by the Fair Market Value of the Stock on such date.
Upon payment in full of the Stock Units, the Stock Units shall be cancelled.

15.      OWNERSHIP OF STOCK RIGHTS.

         By accepting a Stock Right, a Participant acknowledges that one of
the Company's goals in implementing this Plan is to align the interests of
Participants with those of the Company's stockholders, and accordingly agrees
to use his or her best efforts to maintain ownership of the Stock Rights as a
long-term investment. As such, the person(s) who accept(s) such Stock Right
shall represent to the Company, prior to the receipt of Stock Rights, that
such person(s) are acquiring such Stock Rights for their own respective
accounts, for investment, and not with a view to, or for sale in connection
with, the distribution of any such Stock Rights, in which event the person(s)
acquiring such Stock Rights shall be bound by the provisions of the Plan.

         Unless the offering and sale of the Stock Rights shall have been
effectively registered under the Securities Act of 1933, as now in force or
hereafter amended (the "1933 Act"), the Company shall be under no obligation
to issue such Stock Rights unless the following legend is endorsed upon the
certificate(s) evidencing their Stock Rights issued pursuant to such exercise
or such grant:

                  "The shares represented by this certificate have been taken
                  for investment and they may not be sold or otherwise
                  transferred by any person, including a pledgee, unless (1)
                  either (a) a Registration Statement with respect to such
                  shares shall be effective under the Securities Act of 1933, as
                  amended, or (b) the Company shall have received an opinion of
                  counsel satisfactory to it that an exemption from registration
                  under such Act is then available, and (2) there shall have
                  been compliance with all applicable state securities laws."

         At the discretion of the Administrator, the Company shall have
received an opinion of its counsel that the Stock Rights may be issued upon
such particular acceptance in compliance with the 1933 Act without
registration thereunder.

         Each Participant shall continue to comply with the Company's then
applicable insider trading policy and rules with respect to blackout periods and
with all rules and regulations of the Securities and Exchange Commission
applicable to trading in securities by members of the Boards of Directors of
publicly traded companies at all times when making decisions with respect to the
purchase, ownership, and disposition of Stock under this Plan.


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16.      DISSOLUTION OR LIQUIDATION OF THE COMPANY.

         Upon the dissolution or liquidation of the Company, all Stock Rights
which have not been accepted as of such date will terminate and become null and
void; provided, however, that if the rights of a Participant or a Participant's
Survivors have not otherwise terminated and expired, the Participant or the
Participant's Survivors will have the right immediately prior to such
dissolution or liquidation to exercise or accept any Stock Right to the extent
that the Stock Right is exercisable or subject to acceptance as of the date
immediately prior to such dissolution or liquidation.

          Upon the dissolution or liquidation of the Company, a Participant
shall receive, not later than thirty days following the date of the Company's
dissolution or liquidation, a lump sum payment in cash equal to the number of
Stock Units recorded in the Participant's account on the date of such
dissolution or liquidation multiplied by the Fair Market Value of the Stock
on such date. Upon payment in full of the Stock Units, the Stock Units shall
be cancelled.

17.      ADJUSTMENTS.

         Except as otherwise set forth in Section 8 hereof, upon the occurrence
of any of the following events, a Participant's rights with respect to any Stock
Right granted to him or her hereunder shall be adjusted as hereinafter provided,
unless otherwise specifically provided in any applicable Award Agreement:

         A. STOCK DIVIDENDS AND STOCK SPLITS. If (i) the shares of Common Stock
shall be subdivided or combined into a greater or smaller number of shares or if
the Company shall issue any shares of Common Stock as a stock dividend on its
outstanding Common Stock, or (ii) additional shares or new or different shares
or other securities of the Company or other non-cash assets are distributed with
respect to such shares of Common Stock, the number of shares of Common Stock
deliverable upon the exercise or acceptance of such Stock Right may be
appropriately increased or decreased proportionately to reflect such events.

         B. CONSOLIDATIONS OR MERGERS. If the Company is to be consolidated with
or acquired by another entity in a merger, sale of all or substantially all of
the Company's assets or otherwise (an "Acquisition"), the Administrator or the
board of directors of any entity assuming the obligations of the Company
hereunder (the "Successor Board"), shall, with respect to outstanding Stock
Rights, either (i) make appropriate provisions for the continuation of such
Stock Rights by substituting on an equitable basis for the Stock then subject to
such Stock Rights either the consideration payable with respect to the
outstanding Stock in connection with the Acquisition or securities of any
successor or acquiring entity; or (ii) upon written notice to the Participants,
provide that all Stock Rights must be accepted (to the extent then subject to
acceptance) within a specified number of days of the date of such notice, at the
end of which period the offer of the Stock Rights shall terminate.

         C. RECAPITALIZATION OR REORGANIZATION. In the event of a
recapitalization or reorganization of the Company (other than a transaction
described in Subparagraph B above) pursuant to which securities of the Company
or of another corporation are issued with respect to the outstanding shares of
Common Stock, a Participant upon exercising or accepting a Stock Right shall be
entitled to receive for the purchase price, if any, paid upon such exercise or


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acceptance the securities which would have been received if such Stock Right had
been exercised or accepted prior to such recapitalization or reorganization.

         D. ADJUSTMENT TO STOCK UNITS. Upon the happening of any of the
events described in Subparagraphs A, B or C above, the Stock Rights may be
appropriately adjusted to reflect the events described in such Subparagraphs.
The Administrator or the Successor Board shall determine the specific
adjustments to be made under this Section 17 and, subject to Section 4, its
determination shall be conclusive.

18.      ISSUANCES OF SECURITIES.

         Except as expressly provided herein, no issuance by the Company of
shares of stock of any class, or securities convertible into shares of stock of
any class, shall affect, and no adjustment by reason thereof shall be made with
respect to, the number or price of shares subject to Stock Rights. Except as
expressly provided herein, no adjustments shall be made for dividends paid in
cash or in property (including without limitation, securities) of the Company
prior to any issuance of Stock pursuant to a Stock Right.

19.      WITHHOLDING.

         In the event that any federal, state, or local income taxes,
employment taxes, Federal Insurance Contributions Act ("FICA") withholdings
or other amounts are required by applicable law or governmental regulation to
be withheld from the Participant's remuneration in connection with (i) the
exercise or acceptance of a Stock Right or (ii) the cancellation or
liquidation of a Stock Unit, the Company may withhold from the Participant's
compensation, if any, or may require that the Participant advance in cash to
the Company, the statutory minimum amount of such withholdings unless a
different withholding arrangement, including the use of shares of the
Company's Common Stock or a promissory note, is authorized by the
Administrator (and permitted by law). For purposes hereof, the Fair Market
Value of the Stock withheld for purposes of payroll withholding shall be
determined in the manner provided in Section 1 above, as of the most recent
practicable date prior to the date of exercise. If the Fair Market Value of
the Stock withheld is less than the amount of payroll withholdings required,
the Participant may be required to advance the difference in cash to the
Company.

20.      TERMINATION OF THE PLAN.

         The Plan will terminate 10 years after its approval by the shareholders
of the Company. The Plan may be terminated at an earlier date by vote of the
shareholders or the Board of Directors of the Company; provided, however, that
any such earlier termination shall not affect any Award Agreements executed
prior to the effective date of such termination.

21.      AMENDMENT OF THE PLAN AND AGREEMENTS.

         The Plan may be amended by the shareholders of the Company. The Plan
may also be amended by the Administrator, including, without limitation, to the
extent necessary to qualify the stock issuable upon exercise or acceptance of
any outstanding Stock Rights granted, or Stock Rights to be granted, under the
Plan for listing on any national securities exchange or quotation in any
national automated quotation system of securities dealers. Any amendment
approved by


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the Administrator which the Administrator determines is of a scope that requires
shareholder approval shall be subject to obtaining such shareholder approval.
Any modification or amendment of the Plan shall not, without the consent of a
Participant, adversely affect his or her rights under a Stock Right previously
granted to him or her. With the consent of the Participant affected, the
Administrator may amend outstanding Award Agreements in a manner which may be
adverse to the Participant but which is not inconsistent with the Plan. In the
discretion of the Administrator, outstanding Award Agreements may be amended by
the Administrator in a manner which is not adverse to the Participant.

22.      RELATIONSHIP WITH THE COMPANY.

         Nothing in this Plan or any Award Agreement shall be deemed to prevent
the Company from terminating the director status of a Participant, nor to
prevent a Participant from terminating his or her own director status or to give
any Participant a right to be retained in employment or other service by the
Company or any Affiliate for any period of time.

23.      GOVERNING LAW.

         This Plan shall be construed and enforced in accordance with the law of
The Commonwealth of Massachusetts.



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