Exhibit 5.1




                         [Cooley Godward LLP Letterhead]




December 4, 2000

Rigel Pharmaceuticals, Inc.
240 East Grand Avenue
South San Francisco, CA 94080

Ladies and Gentlemen:

You have requested our opinion with respect to certain matters in connection
with the filing by Rigel Pharmaceuticals, Inc. (the "Company") of a
Registration Statement on Form S-8 (the "Registration Statement") with the
Securities and Exchange Commission covering the offering of up to an
aggregate of 8,051,358 shares of the Company's Common Stock, $.001 par value
(the "Shares"), with respect to the Company's 2000 Equity Incentive Plan,
2000 Employee Stock Purchase Plan and 2000 Non-Employee Directors' Stock
Option Plan (collectively, the "Plans").

In connection with this opinion, we have examined the Registration Statement
and related Prospectus, the Company's Amended and Restated Certificate of
Incorporation and By-laws and such other documents, records, certificates,
memoranda and other instruments as we deem necessary as a basis for this
opinion. We have assumed the genuineness and authenticity of all documents
submitted to us as originals, the conformity to originals of all documents
submitted to us as copies thereof and the due execution and delivery of all
documents where due execution and delivery are a prerequisite to the
effectiveness thereof.

On the basis of the foregoing, and in reliance thereon, we are of the
opinion that the Shares, when sold and issued in accordance with the Plans,
the Registration Statement and the related Prospectus, will be validly
issued, fully paid, and nonassessable (except as to shares issued pursuant to
certain deferred payment arrangements, which will be fully paid and
nonassessable when such deferred payments are made in full).

We consent to the filing of this opinion as an exhibit to the Registration
Statement.

Very truly yours,

COOLEY GODWARD LLP



By:      /s/ Suzanne Sawochka Hooper
   -------------------------------------
         Suzanne Sawochka Hooper