Exhibit 32.2

                            CERTIFICATION PURSUANT TO
                            18 U. S. C. SECTION 1350,
                             AS ADOPTED PURSUANT TO
                 SECTION 906 OF THE SARBANES -0XLEY ACT OF 2002

In connection with the Annual Report of GTx, Inc. (the "Company") on Form 10-K
for the period ending December 31, 2004, as filed with the Securities and
Exchange Commission on the date hereof (the "Report"), I, Mark E. Mosteller,
Vice President and Chief Financial 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 results of operations
            of the Company.


/s/ Mark E. Mosteller
- --------------------------------------
Mark E. Mosteller, CPA
Vice President and Chief Financial Officer

March 24, 2005