Laboratory studies suggest that castration-resistant prostate cancer (CRPC) cell growth is suppressed by supraphysiologic doses of testosterone (T). In this study, 12 men received high doses of T transdermally for 7 d, for 4 mo, or until progression.The approach was safe and toxicity was mild, but responses were modest. Because serum T did not reach intended supraphysiologic levels, the authors urged more clinical testing.