Sixty-six per cent of a group of 21 renal transplant recipients with chronic renal failure were shown to have adrenal suppression due to glucocorticoid treatment. Gradual withdrawal of steroids in these patients returning to maintenance dialysis therapy was achieved with few symptoms of hypoadrenalism. Adrenal recovery occurred in 52 per cent of patients after three months and 71 per cent after six months. However, the plasma cortisol response to insulin-induced hypoglycaemia, studied in patients in whom adrenal recovery had been demonstrated, was impaired in 46 per cent of cases. These results indicate that corticosteroids in renal transplant recipients induce profound hypothalamic-pituitary-adrenal suppression which is slow to recover. Such patients returning to maintenance dialysis are at risk of acute adrenocortical insufficiency for several months. Although withdrawal of steroids can be achieved safely, cover during periods of stress should be given until the hypothalamic-pituitary-adrenal axis has been shown to respond normally.