In healthy individuals, ACTH is the major stimulus for cortisol production and cellular growth of the adrenal cortex. Normal or elevated ACTH levels can amplify this stimulus, leading to hypercortisolism and growth of the adrenal gland, a clinical condition recognized as Cushing's syndrome. However, some patients with hypercortisolism of Cushing's syndrome have suppressed rather than normal or high levels of ACTH. This pilot study seeks to better understand the apparently autonomous nature of hypercortisolism in two benign causes of Cushing's syndrome, adrenal adenomas and massive macronodular adrenal disease (MMAD).