To determine whether the increase in aldosterone secretion following constriction of the carotid arteries was due to release of pituitary ACTH, 4 normal dogs, 5 acutely hypophysectomized dogs and 2 acutely hypophysectomized dogs given ACTH by constant infusion were subjected to constriction of both common carotid arteries. A variable rise in aldosterone secretion occurred in dogs with intact pituitaries after carotid constriction, with an associated increase in 17-hydroxycorticoid secretion. In hypophysectomized dogs and in ACTH-infused hypophysectomized dogs, this rise failed to occur. The data support the conclusion that the increase in aldosterone secretion following carotid constriction is due to pituitary release of ACTH.