Pituitary glands of thyroidectomized and intact rats were assayed for ACTH content with and without the application of a stress. The depletion of ACTH from the pituitaries of stressed thyroidectomized rats was no greater than that of similarly treated intact animals. Adrenal glands of operated-stressed animals, however, revealed an increased response to the released ACTH, as evidenced by greater depletions of ascorbic acid, compared to intact-stressed rats. Data indicate a hypersensitivity of the adrenal of the thyroidectomized rat to a given amount of ACTH above the "resting " physiological level.