Introduction A recent paper1 published jointly from this laboratory and that of Dr. John A. Luetscher developed the concept that certain tumors of "nonendocrine" tissues can give rise to Cushing's syndrome through the mechanism of secreting an adrenocorticotropic substance which promotes growth of the adrenal cortices and stimulates the secretion of adrenal steroids. It was demonstrated that patients harboring such tumors had excessive concentrations of adrenocorticotropic material in their plasma and that they secreted excessive quantities of cortisol (hydrocortisone), resulting in high levels of plasma and urinary 17-hydroxycorticosteroids (17-OHCS). The hypersecretion of cortisol could not be suppressed by the administration of exogenous steroids such as dexamethasone. Clinical manifestations varied from patient to patient depending upon such factors as the severity of the endocrinologic disturbance, the duration of the disorder, and the sex of the patient. A sine qua non in the diagnosis of this clinicopathological entity is the demonstration