We describe four cases of primary hyperaldosteronism whose initial presentation was a moderate to severe hypertension. In three patients an adrenal adenoma was found; in another patient was due to unilateral adrenal hyperplasia. A good therapeutic response was achieved in all cases by unilateral adrenalectomy. The captopril test (Lyons version) proved useful to exclude essential hypertension and, may be, in distinguishing the new sub-types of primary hyperaldosteronism recently described. Indeed, only in the case of unilateral adrenal hyperplasia a fall in plasma aldosterone levels was observed. However, we feel that further investigation is needed to clarify this point.