Safety and efficacy of a slow-release formulation of D-Trp-6-luteinising-hormone-releasing-hormone (D-Trp-6-LHRH) microcapsules were compared with orchidectomy in the initial treatment of advanced prostatic carcinoma. 41 patients were randomly assigned to D-Trp-6-LHRH and 38 to orchidectomy. Suppression of testosterone and reduction in prostatic acid phosphatase levels were similar in both groups. 87% of patients in the D-Trp-6-LHRH group and 81% in the orchidectomy group responded to treatment or showed no deterioration. Side-effects related to the decrease in testosterone were similar in both groups. 3 patients given D-Trp-6-LHRH had a disease "flare" in the first ten days of treatment which resolved completely when testosterone fell to castrate levels. Results of psychological assessment were similar in both groups before treatment, and on follow-up there was a weak trend towards decreased psychological morbidity in the hormone group. The slow-release preparation of D-Trp-6-LHRH microcapsules offers an important alternative in the management of advanced prostatic carcinoma.