EXHIBIT 99.1



                  CERTIFICATION BY PRINCIPAL EXECUTIVE OFFICER
                       PURSUANT TO 18 U.S.C. SECTION 1350,
                       AS ADOPTED PURSUANT TO SECTION 906
                        OF THE SARBANES-OXLEY ACT OF 2002


     In connection with the accompanying Quarterly Report on Form 10-Q of Ligand
Pharmaceuticals Inc. for the quarter ended September 30, 2002, I, David E.
Robinson, Chairman, President and Chief Executive Officer of Ligand
Pharmaceuticals Inc., hereby certify pursuant to 18 U.S.C. Section 1350, as
adopted pursuant to Section 906 of the Sarbanes-Oxley Act of 2002, to the best
of my knowledge and belief, that:

     (1) such Quarterly Report on Form 10-Q for the quarter ended September 30,
2002, fully complies with the requirements of section 13(a) or 15(d) of the
Securities Exchange Act of 1934; and

     (2) the information contained in such Quarterly Report on Form 10-Q for the
quarter ended September 30, 2002, fairly presents, in all material respects, the
financial condition and results of operations of Ligand Pharmaceuticals Inc.



Date: November 13, 2002


                             /S/DAVID E. ROBINSON
                             -----------------------------------------
                             David E. Robinson
                             CHAIRMAN, PRESIDENT AND CHIEF EXECUTIVE OFFICER