Exhibit 10.55
       PORTIONS OF THIS DOCUMENT HAVE BEEN OMITTED (DESIGNATED BY AN 
        ASTERIX (*) AND WHITE SPACE) AND FILED SEPARATELY WITH THE
             SECURITIES AND EXCHANGE COMMISSION PURSUANT TO A 
                       REQUEST FOR CONFIDENTIAL TREATMENT
                     FILED JANUARY 31, 1995; FILE NO. 0-15609



                                THIRD AMENDMENT

     Effective January 15, 1995, Agouron Pharmaceuticals, Inc., a California 
corporation with offices at 10350 North Torrey Pines Road, Suite 100, La 
Jolla, California 92037 ("Agouron") and Japan Tobacco Inc., a Japanese 
corporation with offices at 12-62, Higashi-Shinagawa 4 chome, Shinagawa-ku, 
Tokyo 140, Japan ("JT"), for good and valuable consideration, agree as 
follows:


                                   Article I
                                   Background

     1.01     Pursuant to the terms of an agreement which was originally 
entered into on December 18, 1992 (This Agreement, as amended, is hereinafter 
referred to as "Agreement One.").  Agouron and JT have conducted a 
collaborative Research Program ("Research Program One") consisting of * 
                                      to discover, develop, manufacture and 
market novel immunosuppressive drugs.  On February 28, 1994, Agouron and 
JT entered into the First Amendment of Agreement One.  On April 22, 
1994, Agouron and JT entered into the Second Amendment and Restatement 
of Agreement One.  

     1.02     Agouron and JT are also conducting two additional Research 
Programs ("Research Program Two" and "Research Program Three") focusing on 
the development of anti-viral drugs in accordance with the provisions of 
agreements which were originally entered into on February 28, 1994 
("Agreement Two" and "Agreement Three").

     1.03     *  


                                       To affect the preceding and to clarify 
the parties' rights and obligations, the parties agree to further amend 
the terms of Agreement One by entering into this Third Amendment to 
Agreement One ("Third Amendment").

     1.04     For purposes of this Third Amendment, terms with initial 
capitalization shall have the same meanings as those set out in Agreement 
One.

                                 Article II
                               Third Amendment

     2.01     The parties agree that the last day of the Research Term of 
Agreement One is January 15, 1995 and that Research Program One ended on 
January 15, 1995.


     2.02     The parties agree that only chemical compounds which have been
shown by or on behalf of Agouron or JT, independently or jointly, on or 
before the last day of the Research Term to *                            
         shall be eligible to be Program Compounds, and that any chemical 
compounds synthesized after January 15, 1995 shall not be eligible to be 
Program Compounds.

     2.03     The parties agree that no Program Compounds or Program Products 
were conceived and/or invented in Research Program One during the Research 
Term.

     2.04     The parties agree that the chemical compounds contained in the 
List of Research Program One Compounds dated as of January 15, 1995 are not 
Program Compounds or Program Products.  

     2.05     The parties agree that the parties' rights and obligations 
regarding the commercialization of any chemical compounds and intermediates 
thereof which were invented in Research Program One including, but not 
limited to, the chemical compounds contained in the List of Research Program 
One Compounds dated as of January 15, 1995, and any products incorporating 
such chemical compounds, are set forth in Section 3.05(g) of the Second 
Amendment and Restatement of Agreement One, which Section 3.05(g) reads 
in full as follows:

              (g)  Unless the parties agree otherwise, any chemical 
                   compound(s) which is *

                                                                     
                                                                      
                       The parties shall                    *       
                     the most *
                                                  
                                                                Each 
                    party, as *                     shall have the *




     2.06     The parties agree that *                            does not 
include any know-how, trade secret, experimental data, formula, expert 
opinion, experimental procedure and other confidential and/or proprietary 
information *
     
     
which is *
        as the case may be, *

     2.07     The parties shall cause their respective employees to cooperate 
as reasonably required to co-author manuscripts and to file patent 
applications on separately or jointly made inventions arising out of 
Agreement One.

     2.08     The parties agree that Research Project II is canceled 
effective January 15, 1995.  *




     2.09     The parties agree to end Research Project I effective 
January 15, 1995 and to reallocate the research efforts which were to be 
committed by Agouron scientists during the third year of Research Project I 
to Research Programs Two and Three.  Notwithstanding the reallocation of 
Agouron's research efforts, *



     2.10     Commencing *                                             
without any further action *
     
     
                               on its own or with any third party, *
     
     
     agrees not to *
     
                         agrees not to *                               
         The 

     
     parties hereby agree that any *
     
                                      If requested by  *
     
     

     2.11     Except as modified by the terms contained herein, the 
provisions of Agreement One shall remain in full force and effect.

     2.12     Notwithstanding the *
     
                     hereby confirms that such *
     


AGOURON PHARMACEUTICALS, INC.                 JAPAN TOBACCO INC.

By     /S/ R. Kent Snyder                     By     /S/ Tsuyoshi Sasaki     

Name   R. Kent Snyder                         Name   Tsuyoshi Sasaki        

Title  Vice President, Business Development   Title   Executive Director     

Date   January 26, 1995                       Date   January 26, 1995