EXHIBIT 32.1

                            OSI PHARMACEUTICALS, INC.

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

In connection with the Quarterly Report of OSI Pharmaceuticals, Inc. (the
"Company") on Form 10-Q for the period ended March 31, 2004 as filed with the
Securities and Exchange Commission on the date hereof (the "Report"), I, Colin
Goddard, Ph.D., Chief Executive Officer of the Company, certify, pursuant to 18
U.S.C. Section 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.

Date: May 14, 2004                           /s/ Colin Goddard, Ph.D.
                                             -----------------------------------
                                             Colin Goddard, Ph.D.
                                             Chief Executive Officer

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