In dogs with hypothalamic lesions as well as in intact and hypophysectomized dogs, adrenal venous blood samples were collected and analyzed for 17-hydroxycorticosteroids (17-OHCS). In intact dogs a marked increase in adrenal 17-OHCS secretion was observed following the i.v. infusion of cyanide as well as after the i.v. injection of pilocarpine; this was completely abolished by hypophysectomy. The adrenocortical response to pilocarpine was markedly impaired and that to cyanide partially suppressed after lesioning of the anterior median eminence. However, after lesioning of the posterior median eminence, the adrenocortical secretory response to pilocarpine was almost the same as in intact dogs, whereas the response to cyanide was markedly impaired. Thus, a dissociation of adrenocortical secretory responses to cyanide and pilocarpine was demonstrated in dogs with hypothalamic lesions.