Exhibit 5
                                                                    ---------

                                               October 9, 2001

Synaptic Pharmaceutical Corporation
Board of Directors
215 College Road
Paramus, New Jersey 07652
Gentlemen:

     We have acted as special counsel for Synaptic  Pharmaceutical  Corporation.
(the  "Company") in  connection  with the  preparation,  execution and filing of
Post-effective  Amendment  No. 2 to Form S-8  Registration  Statement  under the
Securities Act of 1933 relating to the  registration of an additional  1,500,000
shares of the Company's common stock, $.01 par value ("Common Stock"), which may
be issued pursuant to the Company's 1996 Incentive Plan, as amended and restated
(the "Plan").

     In connection with the opinion  expressed  below, we have made such factual
inquiries and have examined or caused to be examined such documents, records and
instruments  and  such  questions  of law as we  have  considered  necessary  or
appropriate for the purpose of such opinion.  On the basis of such inquiries and
examinations,  it is our opinion  that any newly  issued  shares of Common Stock
issued by the Company in accordance  with the terms of the Plan, will be legally
issued, fully paid and non-assessable.

     We consent to the filing of this opinion as an exhibit to the  Registration
Statement  referred  to above.  In so doing,  we do not admit that we are in the
category of persons whose consent is required  under Section 7 of the Securities
Act of  1933  or the  rules  and  regulations  of the  Securities  and  Exchange
Commission promulgated thereunder.


                                               Very truly yours,

                                               Baker Botts L.L.P.