Prostate cancer is a common cancer in men that is exquisitely sensitive to the effects of hormonal withdrawal. Tonic GnRH stimulation with an LHRH agonist should result in complete suppression of LH secretion and subsequent ablation of testosterone production by the testes. Hydrogel implants containing histrelin, a potent GnRH agonist, have been implanted in 9 men with prostate cancer who had clinical indications for hormonal suppression. Prompt and reliable suppression of hormonal production with biochemical and clinical evidence of prostate cancer regression were documented for the patients treated. No specific side effects of histrelin treatment, outside of those expected with any hormonal suppression, were seen in this study. Patients have been treated for over 3 years with histrelin hydrogel implants with reliable testosterone suppression. Since current medical treatments for suppression of testosterone secretion in prostate cancer patients involve monthly injections, this therapy holds significant promise as the primary therapy for patients with systemic prostate cancer.