EXHIBIT 32.2

                           OSI PHARMACEUTICALS, INC.

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

     In connection with the Annual Report of OSI Pharmaceuticals, Inc. (the
"Company") on Form 10-K for the period ended September 30, 2004 as filed with
the Securities and Exchange Commission on the date hereof (the "Report"), I,
Robert L. Van Nostrand, Vice President and Chief Financial Officer of the
Company, certify, pursuant to 18 U.S.C. sec. 1350, as adopted pursuant to
Section 906 of the Sarbanes-Oxley Act of 2002, that:

     (1) The Report 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 the Report fairly presents, in all
material respects, the financial condition and result of operations of the
Company.

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                                                        /s/ ROBERT L. VAN NOSTRAND
                                               ---------------------------------------------
                                                          Robert L. Van Nostrand
                                                Vice President and Chief Financial Officer

Date: December 13, 2004
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