Ninety-five patients with stage C (C1 + C2) or D (D1 + D2) prostatic carcinoma were treated with the depot formulation of D-TRP-6 LH-RH ("Decapeptyl") for up to 33 months. Serum testosterone (T) levels were significantly reduced to castration levels within 4 weeks and maintained persistently low. Similarly, LH levels were decreased, although they remained in the normal range. Stimulation tests with either Gn-RH or HCG in course of treatment showed the achievement of a complete pituitary desensitization and almost a complete down-regulation of testicular LH receptors. Of 88 patients evaluable for response, about one-half showed an objective response. In most cases, subjective improvement with relief of bone pain and/or urinary symptoms was obtained without major side effects. These results indicate that the depot formulation of D-TRP-6 LH-RH offers an effective therapeutic alternative for patients with advanced prostatic cancer.