Adrenal venous blood samples were collectedfrom conscious and anesthetized dogs before and after an injection of pilocarpine and were analyzed for 17-hydroxycorticosteroids (17-OHCS). In conscious dogs the adrenal 17-OHCS secretion rate increased from a pre-injection secretion rate of 0.11 ± 0.014 to 1.58 ± 0.069 (mean ± SE) µg/kg/min following an intravenous injection of pilocarpine (0.3 mg/kg); there was a return to the baseline level by 120 min. In anesthetized dogs a marked increase in adrenal 17-OHCS secretion was also observed, which was completely abolished by hypophysectomy. A noticeable impairment of the adrenocortical response to pilocarpine was found to be produced by radio-frequency-current lesions of the anterior median eminence. A partial depression of the response was also observed in dogs with the anterior ventromedial hypothalamic lesions. Lesions destroying other hypothalamic areas were found to be without significant effect upon the adrenal cortical secretory response to pilocarp