[Millennium logo]                                       EXHIBIT 10.1


   MILLENNIUM PHARMACEUTICALS, INC.
   40 Landsdowne Street
   Cambridge, Massachusetts 02139
   617.679.7000
   www.millennium.com


August 6, 2004

Marsha H. Fanucci
Millennium Pharmaceuticals, Inc.
40 Landsdowne Street
Cambridge, MA 02139

Dear Marsha:

This letter documents the agreement between you and Millennium Pharmaceuticals,
Inc. ("Millennium" or the "Company"), made in consideration of continued
employment by you and for other good and valuable consideration, the receipt and
sufficiency of which are hereby acknowledged, concerning the terms of a
severance payment payable to you under certain conditions as described below.

1.   In the event that your employment is terminated by Millennium other than
     for Justifiable Cause (as defined below), Millennium will pay you a
     severance payment (the "Severance Payment") equal to twelve (12) months'
     base salary, at your then current rate of pay (but no less than your base
     salary as in effect on May 1, 2004). The Severance Payment will be payable
     periodically in accordance with Millennium's payroll procedures as then in
     effect, commencing with the first payroll period following termination of
     employment. In the event your employment is terminated by Millennium for
     Justifiable Cause or voluntarily by you, you will not be entitled to any
     Severance Payment.

2.   "Justifiable Cause" shall mean the occurrence of any of the
     following events: (i) your conviction of, or plea of nolo contendere with
     respect to a felony or a crime involving moral turpitude, (ii) your
     commission of an act of personal dishonesty or breach of fiduciary duty
     involving personal profit in connection with the Company, (iii) your
     commission of an act, or failure to act, which the Board of Directors of
     the Company shall reasonably have found to have involved willful misconduct
     or gross negligence on your part, in the conduct of your duties as an
     employee of the Company, (iv) habitual absenteeism, alcoholism or drug
     dependence on your part which interferes with the performance of your
     duties as an employee of the Company, (v) your willful and material failure
     or refusal to perform your services as an employee of the Company, (vi) any
     material breach by you to fulfill the terms and conditions under which you
     are employed by the Company, or (viii) your willful and material failure or
     refusal to carry out a direct request of the Board of Directors or Chief
     Executive Officer. In the event that Millennium terminates your employment
     for Justifiable Cause, Millennium will provide you with a statement of the
     basis for such termination and an opportunity to respond thereto.

3.   The payment to you of the amounts payable under Paragraph 1 shall be
     conditioned upon the execution by you of a release in the form provided by
     the Company and shall constitute your sole remedy in the event of your
     termination of employment in the circumstances set forth in Paragraph 1.

4.   This agreement may be amended or modified only by a written instrument
     executed by you and Millennium. This agreement will be interpreted and
     enforced in accordance with the laws of the Commonwealth of Massachusetts.

5.   Any notice delivered under this agreement shall be deemed duly delivered
     when personally delivered, or four business days after it is sent by
     registered or certified mail, return receipt requested, postage prepaid, or
     one business day after it is sent for next-business day delivery via a
     reputable nationwide overnight courier service to the Company at 40
     Landsdowne Street, Cambridge, MA 02139, Attn: Vice President of Human
     Resources, or to you at your address as listed above. Either party may
     change the address to which notices are to be delivered by giving notice of
     such change to the other party in the manner set forth in this paragraph.

6.   This agreement constitutes the entire agreement between the parties with
     respect to the subject matters hereof, and supersedes all prior agreements
     and understandings, whether written or oral, with respect to such subject
     matters.

7.   This agreement shall be binding upon and inure to the benefit of both
     parties and their respective successors and assigns, including any
     corporation with which, or into which, the Company may be merged, or which
     may succeed to the Company's assets or business, provided, however, that
     your obligations to the Company are personal and shall not be assigned.

Please acknowledge your agreement by countersigning this letter below.

                        Sincerely,
                        MILLENNIUM PHARMACEUTICALS, INC.

                        By: /s/ MARK J. LEVIN
                            Mark J. Levin
                            Chairperson, President and Chief Executive Officer
AGREED TO:

/s/ MARSHA H. FANUCCI
Marsha H. Fanucci

Dated: AUGUST 6, 2004