EXHIBIT 32.2

                            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 Annual Report of GTx, Inc. (the "Company") on Form 10-K
for the year ended December 31, 2005, as filed with the Securities and Exchange
Commission on the date hereof (the "Report"), I, Mark E. Mosteller, Chief
Financial Officer of the Company certify, pursuant to Rule 13a-14(b) or Rule
15d-14(b) and 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.

Date:  March 2, 2006

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

This certification accompanies the Form 10-K to which it relates, is not deemed
filed with the Securities and Exchange Commission and is not to be incorporated
by reference into any filing of the Company under the Securities Act of 1933, as
amended, or the Securities Exchange Act of 1934 (whether made before or after
the date of the Form 10-K), irrespective of any general incorporation language
contained in such filing.