A 58-yr-old woman had frequent hypoglycemic attacks, undetectable levels of plasma cortisol, ACTH, and β-lipotropin, and deficient responses of these hormones after insulin induced-hypoglycemia and metyrapone. Her GH responses to arginine infusion were normal as were her gonadotropin responses to LRH. Her TSH and PRL responses to TRH were abnormally high. Anaphylactic shock occurred after the injection of either synthetic ACTH-Z-(l–24) (Cortrosin-Z) or ACTH-(1–18) (Acthormone). She had received two prior injections of synthetic ACTH-Z-(l–24) 2 months earlier. Circulating anti- ACTH antibody was found in her plasma by radioimmunological methods, but this antibody did not prevent corticosterone production by ACTH in an in vitro ACTH bioassay system. The pathogenic significance of this antibody in the ACTH deficiency is doubtful, and the etiology of the isolated ACTH and β-LPH deficiency is not clear.