Exhibit 99.1
                                                                 ------------

                                 Certification
           Pursuant to Section 906 of the Sarbanes-Oxley Act of 2002
                   (Subsections (a) and (b) of Section 1350,
                  Chapter 63 of Title 18, United States Code)

     Pursuant to Section 906 of the  Sarbanes-Oxley Act of 2002 (subsections (a)
and (b) of section 1350,  chapter 63 of title 18,  United States Code),  each of
the  undersigned  officers of Synaptic  Pharmaceutical  Corporation,  a Delaware
corporation (the "Company"),  does hereby certify, to such officer's  knowledge,
that:

     The Quarterly  Report on Form 10-Q for the quarter ended September 30, 2002
(the "Form 10-Q") of the Company fully complies with the requirements of Section
13(a) or 15(d) of the Securities Exchange Act of 1934 and information  contained
in the Form 10-Q  fairly  presents,  in all  material  respects,  the  financial
condition and results of operations of the Company.


November 14, 2002                          /s/ Kathleen P. Mullinix
                                           -----------------------------------
                                           Name: Kathleen P. Mullinix
                                           Title: President and
                                                   Chief Executive Officer

November 14, 2002                          /s/ Edmund M. Caviasco
                                           -----------------------------------
                                           Name: Edmund M. Caviasco
                                           Title: Controller and
                                                   Principal Accounting Officer

     The foregoing  certification  is being furnished solely pursuant to Section
906 of the  Sarbanes-Oxley Act of 2002 (subsections (a) and (b) of section 1350,
chapter 63 of title 18,  United  States  Code).