Abnormalities in hypothalamic-pituitary adrenal axis function were demonstrated by measuring plasma adrenocorticotropin abnormal concentrations following Vasoactive Intestinal Peptide (VIP) and Corticotropin Releasing Hormone (CRH) administration during a phase of remission of Cushing's disease in a 45-year-old female patient. When observed 80 days after the first examination, the patient no longer showed cushingoid features and serum cortisol and plasma ACTH were not abnormally high. VIP infusion (75 micrograms during 12 min) induced a significant increase in serum cortisol and ACTH plasma levels with respect to the normal unresponsiveness. Exaggerated plasma ACTH response to CRH (50 micrograms iv) was also observed. We conclude that the study of ACTH and cortisol response to VIP and CRH may be useful in revealing Cushing's disease even during a remission phase of the disorder.