Hypothalamic pituitary function was evaluated in seven patients with Cushing's disease. In all subjects there was an absence of GH elevation following hypoglycemia. Three patients demonstrated basal hyperprolactinemia. Six had an intact PRL rise following TRH. However, four patients failed to show PRL elevation with insulin hypoglycemia and six were unresponsive to chlorpromazine. Five patients showed impaired TSH response to TRH. Many of the subjects had low basal LH and FSH levels. Attenuated or absent gonadotropin responses to LHRH were noted in three females. One male demonstrated an exaggerated FSH response to LHRH. These results indicate that multiple abnormalities of anterior pituitary hormone secretion characterize Cushing's disease.