Luteinizing hormone releasing hormone agonists presently are being evaluated in the treatment of patients with metastatic prostatic cancer. To determine the comparative benefits of a specific luteinizing hormone releasing hormone agonist [6-leu (1-9) luteinizing hormone releasing hormone nonapeptide ethylamide] relative to conventional estrogen therapy 23 patients with stage D2 prostatic cancer were randomized to receive either 1 mg. luteinizing hormone releasing hormone agonist daily (12) or 3 mg. diethylstilbestrol per day (11). Both agents were effective in inducing a remission in all patients, although diethylstilbestrol was slightly faster. The early phase of treatment with the luteinizing hormone releasing hormone agonist was dominated by a transient reversible deterioration (the flare) of the patient, which was believed to be related to the agonist-induced increase in serum androgens. At 1 year of followup adverse effects in both groups have been minor but the proportion of patients with progression in the luteinizing hormone releasing hormone agonist group (6 of 12) was significantly higher than that in the diethylstilbestrol group (0 of 11). Further investigation is required to determine the role of luteinizing hormone releasing hormone agonist in the treatment of patients with advanced prostatic cancer.