EXHIBIT 32.1

           CERTIFICATION PURSUANT TO RULE 13a-14(b) OR RULE 15d-14(b)
       OF THE SECURITIES EXCHANGE ACT OF 1934 AND 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 on Form 10-Q of Penwest
Pharmaceuticals Co. (the "Company") for the period ended September 30, 2003 as
filed with the Securities and Exchange Commission on the date hereof (the
"Report"), the undersigned, Tod R. Hamachek, Chief Executive Officer of the
Company hereby certifies, pursuant to 18 U.S.C. Section 1350, 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 results of operations of the
Company.

Dated: October 30, 2003                                /s/ Tod R. Hamacheck
                                                       --------------------
                                                       Tod R. Hamachek
                                                       Chairman of the Board and
                                                       Chief Executive Officer

         A signed original of this written statement has been provided to the
Company and will be retained by the Company and furnished to the Securities and
Exchange Commission or its staff upon request.

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