Hormone refractory prostate cancer remains an incurable disease and the discovery of newer agents with higher cytotoxic activity is required. Gossypol is a phenolic compound isolated from cottonseed oil which has been shown to have anti-spermatogenic effects. In in vitro studies, gossypol appears to inhibit the growth of rat prostate cancer cell line MAT-LyLu and human prostate adenocarcinoma cell lines PC-3, LNCaP and DU-145. In vive, gossypol appeared to inhibit tumor growth of subcutaneously implanted MAT-LyLu cells in Copenhagen rats. Gossypol may be an active agent for the treatment of hormone refractory metastatic prostate cancer.