The efficacy and tolerability of Casodex, a new non-steroidal antiandrogen, were studied in 267 patients with advanced prostate cancer. All patients received Casodex, 50 mg daily, as monotherapy. The objective response rate was 55.5% and the subjective response rate was 56.1%. The most common adverse events were the expected pharmacological effects of breast tenderness, gynecomastia and hot flushes. No other adverse events were reported in more than 5% of patients. There was minimal occurrence of impotence, loss of libido and diarrhea. The results show that Casodex 50 mg is effective and well tolerated in the treatment of advanced prostate cancer.