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                                                                EXHIBIT 10.8

                               AMENDMENT NO. 1 TO
               AMENDED AND RESTATED BINDING AGREEMENT IN PRINCIPLE

         THIS AMENDMENT NO. 1 TO AMENDED AND RESTATED BINDING AGREEMENT IN
PRINCIPLE (this "AMENDMENT") is entered into by and between PRAECIS
PHARMACEUTICALS INCORPORATED, a Delaware corporation with its principal place of
business at 1 Hampshire Street, Cambridge, Massachusetts 02139-1572 ("Praecis"),
and Amgen Inc., a Delaware corporation with its principal place of business at
One Amgen Center Drive, Thousand Oaks, California 91320-1789 ("Amgen").

         WHEREAS, the parties have entered into an Amended and Restated Binding
Agreement in Principle (the "Agreement") effective as of March 8, 1999 (the
"Signing Date"), whereby the parties have entered into a collaboration
respecting the research, development and commercialization of certain LHRH
antagonist compounds;

         WHEREAS, the parties desire to amend the Agreement with respect to
certain terms and conditions relating to ownership of regulatory filings and
product licenses relating to LHRH antagonist compounds;

         NOW, THEREFORE, for good and valuable consideration, the parties hereby
agree as follows:

         1. AMENDMENT OF SECTION 14d) OF AGREEMENT. Section 14d) of the
Agreement is hereby amended and restated in its entirety as follows:

                  "d) OWNERSHIP OF REGULATORY FILINGS AND LICENSES. Initially
         Praecis shall file and be the owner and party of record sponsoring all
         regulatory filings (INDs, PLAs, BLAs, ELAs and NDAs or other equivalent
         filings) and product licenses with respect to Licensed Products for the
         prostate cancer and endometriosis indications in the Field of Use in
         the United States. Such ownership and control for the prostate cancer
         indication shall be immediately transferred and assigned to Amgen upon
         NDA approval of such indication for any Licensed Product in the United
         States; PROVIDED, HOWEVER, that at Amgen's option such ownership and
         control may be transferred before such NDA approval anytime following
         (a) Amgen's completion of its $175 MM funding obligation, and upon any
         material delay, as determined by Amgen, in the filing or approval of
         the NDA for prostate cancer (by way of example and not of limitation, a
         requirement by the FDA that an additional study be completed as a
         condition to NDA filing or approval), (b) January 15, 2001, if the NDA
         filing for prostate cancer has not been made prior to such date, or (c)
         January 1, 2002. In case of any of (a), (b) or (c), such option shall
         be exercised by Amgen providing Praecis with written notice no less
         than sixty (60) days prior to the specified date of transfer. Such
         ownership and control for the endometriosis indication shall be
         immediately transferred and assigned to Amgen upon the earlier of (1)
         NDA approval of the first indication for any Licensed Product in the
         United States or (2) September 1, 2000. For each of prostate cancer and
         endometriosis, each party shall


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         permit the other party to cross reference its INDs as necessary
         consistent with final decision making authority in subsection c)
         above. Amgen will file INDs for all indications other than
         prostate and endometriosis and Praecis shall permit Amgen to cross
         reference Praecis' INDs as necessary consistent with final
         decision making authority in subsection c) above. Each party shall
         inform, cooperate with and assist the other with respect to all
         material communications to or from regulatory authorities and both
         parties shall have the right to attend all FDA meetings and
         participate in all telephone calls with the FDA. Amgen and Praecis
         will have equal and complete access to the ongoing clinical trial
         databases for prostate cancer and endometriosis. For each clinical
         trial the parties will establish a corresponding master database
         for the data. When Amgen obtains final decision making authority
         for an indication, master databases for such indication shall be
         transferred by Praecis to Amgen. Outside the United States, Amgen
         shall have ownership and control of all regulatory filings and
         licenses in the Licensed Territory."

         2. EFFECT OF AMENDMENT. The Agreement shall remain in full force and
effect in accordance with its terms, as such terms are expressly amended by this
Amendment.

         3. DEFINITIONS. Capitalized terms not otherwise defined herein shall
have their respective meanings in the Agreement.

         4. GOVERNING LAW. This Amendment shall be governed by the laws of the
State of California, without reference to the conflicts of law principles
thereof.


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         IN WITNESS WHEREOF, duly authorized representatives of the parties have
duly executed this Amendment as of the Signing Date.

PRAECIS PHARMACEUTICALS INCORPORATED

By:      /s/  Marc A. Silver
      ---------------------------------------
Name:    Marc A. Silver
Title:   Vice President, Corporate Development

AMGEN INC.

By:      /s/ Fabrizio Bonanni
      -----------------------------------------
Name:    Fabrizio Bonanni
Title:   Senior Vice President, Quality and Compliance