Hypothalamo-pituitary--adrenal (HPA) function was studied using tetracosactrin and insulin hypoglycemia tests in eleven asthmatic patients who were receiving or had taken oral steroids. The patients had been on prednisone, 5--20 mg/day for 2--17 years. As the dose was reduced they used beclomethasone inhalation, up to 800 micrograms/day. Seven insulin hypoglycemia tests were performed when the patients had been off oral steroids for 15--37 months. Plasma cortisol responses were normal in all seven, three had subnormal responses of ACTH. In five patients serial tetracosactrin and insulin hypoglycaemia tests were performed during reduction of steroid dose. Two patterns of recovery of HPA function were observed. In one, both hypothalamo--pituitary and adrenal function seemed to return simultaneously, in the other normal response to tetracosactrin appeared before that to insulin hypoglycaemia. One patient had normal ACTH and cortisol responses to the stress of a vasovagal attack, but failed to respond to subsequent hypoglycaemia. We conclude that a normal response to tetracosactrin does not indicate recovery of the HPA axis after stopping prolonged oral steroid therapy for asthma, and that patients should continue to carry steroid therapy cards for at least 5 years after such treatment has been discontinued.