A 37 year old black female presented with congestive cardiac failure, 2 months postpartum. She developed spontaneous hypoglycaemia and symptoms of acute adrenal crisis (hypotension, nausea, abdominal pain and tachycardia with small thready pulse), which responded to i.v. dextrose, sodium chloride and hydrocortisone. Biochemical investigations revealed low serum cortisol and plasma adrenocorticotrophic hormone (ACTH) levels. The patient initially showed an impaired cortisol response to intramuscular aqueous tetracosactrin, but an exuberant response after priming with intramuscular tetracosactrin depot. These findings, together with the normal remaining pituitary function, led us to conclude that this patient had isolated ACTH deficiency associated with congestive cardiac failure and acute adrenal crisis.