SOME of the clinical signs and symptoms of Cushing's syndrome are frequently seen in patients who are not taking or producing excessive amounts of glucocorticoids.1 It is not surprising, therefore, that Cushing's syndrome, although rarely encountered, is a frequently suspected diagnosis. Because clinical findings alone are frequently not sufficient to confirm or exclude this diagnosis with confidence, laboratory investigations must be performed on many patients in whom the diagnosis is considered.1 At present, determination of the plasma concentration of 17-hydroxycorticosteroids (17-OHCS) and the 24-hour urinary excretion of 17-OHCS or 17-ketogenic steroids are commonly employed as screening tests for Cushing's syndrome. Unfortunately, the results of these tests in normal subjects and in obese patients overlap those of patients with Cushing's syndrome.2-4 A simple reliable laboratory test for identification of patients with Cushing's syndrome would be advantageous. The purpose of this report is to review our experience with a