The agonist analogues of the gonadotrophin-releasing hormone now provide an alternate medical treatment of prostatic cancer. For effect repeated administration is required, either by five or six times daily intranasal or once daily subcutaneous treatment. There is an obvious disadvantage to such regimens in elderly patients who may have difficulty complying with therapy. In order to circumvent these difficulties, sustained release formulations of the agonist analogues have been synthesized. We report the first clinical use of a long-acting formulation of D-Ser (TBU)6-LHRH Ethylamide (buserelin) using a novel polymer material. Twelve symptomatic patients with previously untreated carcinoma of the prostate were treated with depot buserelin, administered once monthly. In all patients, depot buserelin suppressed serum testosterone into the range seen in castrate men at a rate equivalent to that provided by five times daily intranasal therapy. No significant increase in serum testosterone, luteinizing hormone or follicle-stimulating hormone concentrations occurred during the period of follow-up. Long-acting formulations of buserelin offer an advance in the management of prostatic cancer with agonist analogues of the gonadotrophin-releasing hormone.