Thirty-one patients with advanced metastatic carcinoma of the prostate were treated with the antiestrogen tamoxifen. Of these patients, 29 were refractory to prior hormonal manipulation with estrogens and/or orchiectomy and five achieved an objective response (partial regression of stable disease using National Prostatic Cancer Project criteria). Median survival of the responders was significantly longer than that of the nonresponders (P < 0.05). Two additional patients who had not previously received hormonal therapy both responded, for an overall response rate of 23% (seven of 31 patients). Toxicity was minimal and no tumor flares were reported. These preliminary results support the further clinical trial of tamoxifen in advanced cancer of the prostate.