Exhibit 5.1


                                                December 15, 2000

Affymetrix, Inc.
3380 Central Expressway
Santa Clara, California 95051

            RE: OPINION OF COUNSEL

            I am Senior Vice President and General Counsel of Affymetrix, Inc.,
a Delaware corporation (the "Company"). In that capacity, I am rendering this
opinion in connection with the registration by the Company of the offer and
resale of an aggregate of 1,285,237 shares of Common Stock, $0.01 par value (the
"Shares"), pursuant to the Company's Registration Statement on Form S-3 (the
"Registration Statement") filed with the Securities and Exchange Commission on
the date hereof, on behalf of certain selling stockholders named therein (the
"Selling Stockholders"). The Shares consist of shares that have been issued by
the Company in a private placement.

      In arriving at the opinion expressed below, I have examined and relied
upon originals or copies, certified or otherwise identified to my satisfaction,
of such records of the Company, agreements and other instruments, certificates
of officers and representatives of the Company, certificates of public officials
and other documents as I have deemed necessary or appropriate as a basis for the
opinions expressed herein. In connection with my examination, I have assumed the
genuineness of all signatures, the authenticity of all documents tendered to me
as originals, the legal capacity of all natural persons and the conformity to
original documents of all documents submitted to me as certified or photostatic
copies.

     Based on the foregoing, and subject to the qualifications and limitations
stated herein, it is my opinion that the Shares being registered for resale by
the Selling Stockholders under the Registration Statement have been duly
authorized, validly issued, fully paid and nonassessable.

         I express no opinion with respect to laws other than those of the
federal law of the United States of America, the Delaware General Corporation
Law, and the California Corporation Code and I assume no responsibility as to
the applicability thereto, or the effect thereon, of the laws of any other
jurisdiction.

         I hereby consent to the filing of this opinion as an Exhibit to the
Registration Statement with respect to the Shares under the Securities Act of
1933, as amended.

                              
                                  Very truly yours,

                                  /s/  Vern Norviel

                                       Vern Norviel
                                       Senior Vice President and
                                       General Counsel