SUMMARY A patient is described who showed evidence of 25 years' duration of intermittent hyperadrenocorticalism due to adrenocortical hyperplasia. The most pronounced clinical symptom was oedema formation, which was shown to be associated with phases of increased adrenocortical activity. Cortisol secretion rates, for example, ranged from 24 to 161 mg./24 hr. There was also potassium depletion. The response to dexamethasone was repeatedly anomalous, there being a tenfold increase in excretion of urinary 17-hydroxycorticosteroids. Responses to metyrapone and pyrogen were absent but the response to insulin appeared excessive. There was no alteration by dexamethasone in vitro of synthesis of cortisol or corticosterone. Binding of plasma cortisol and corticosteroid-binding globulin were decreased.