During a 2-year period, 37 patients with symptomatic metastatic prostatic cancer were included in a prospective randomized phase-III trial. Nineteen patients were randomized to subcapsular orchiectomy, and 18 to cyproterone acetate (CPA) treatment with a dose of 50 mg b.i.d. The median age of the patients was 74 years (range 48-88 years), with no differences between the treatment groups. At 3, 6, and 12 months after initiation of the therapy and then every 6 months, patients were clinically and biochemically examined, and isotope scans and X-rays were performed. All patients were followed until death. Relief from symptoms was found following 3 months of treatment in 70.6% (95% confidence limits = 44.0-89.7%) of the patients treated with CPA, and in 83.3% (95% confidence limits = 58.6-96.4%) of the orchiectomized patients. The median time to relapse was 9 months in the CPA group, and 11 months in the orchiectomy group (p greater than 0.05). The median survival time was 13 months, with no differences between the groups. The treatment of advanced prostatic cancer with CPA is found to be a valuable alternative to orchiectomy.