Forty-one patients with prostatic cancer were treated with DTrp6 LH-RH, a luteinizing hormone releasing hormone agonist. Thirty-eight of them had advanced cancer with either metastases or major local spread. In all cases with plasma testosterone levels were normal before treatment, the LH-RH agonist brought them down to values observed after surgical castration. An objective response ("improvement" or "stabilization") was obtained in 68% of the patients, but virtually all "improved" patients were those without previous hormonal treatment. As with all LH-RH agonists, the pharmacological castration produced by DTrp6 LH-RH is of considerable value in the treatment of prostatic cancer, especially since this compound, unlike estrogens, does not seem to cause cardiovascular accidents. However, transient hyperandrogenism may occur during the first days of treatment (as it did in 9 of our patients) and may be responsable for an acute flare-up of the tumoral process, as suggested by 2 of our cases. The concomitant administration of an anti-androgenic drug should perhaps be considered.