Selective adrenal vein catheterization was done on intact and castrated men with prostatic carcinoma. Adrenal to peripheral venous testosterone gradients were observed in all patients, indicating adrenal production of this hormone. No compensatory adrenal production of testosterone was noted during a 17-month period after orchiectomy. The data suggest that the human adrenal in castrates produces testosterone, which may explain why adrenal ablation can offer palliation in some patients with prostatic carcinoma.