Serum follicle-stimulating hormone (FSH), luteinizing hormone (LH), testosterone and testosterone binding affinity (TBA) were measured in 15 uremic males. The mean control serum testosterone level was 262 ng/100 ml. The testosterone value doubled during acute stimulation with human chorionic gonadotropin (HCG) 4000 U daily, a normal percentage increase. Although LH was significantly elevated, the elevation was inadequate to promote normal Leydig cell function in most instances. This impaired pituitary-Leydig cell mechanism was found in association with a normal TBA. Acute increases in serum testosterone produced by HCG did not alter TBA from control values.