The diagnosis of primary tumoral hyperaldosteronism is based on a series of hormonal parameters, measured under resting conditions and after stimulation. The results of the administration of a single dose of a converting enzyme inhibitor, Captopril (1 mg/kg body weight per os), can support this diagnosis. In contrast to essential hypertension and hyperaldosteronism due to bilateral adrenal hyperplasia, plasma aldosterone levels remain unchanged in tumoral hyperaldosteronism after administrating Captopril. This is a simple test which can be performed in a morning which clearly differentiated 8 cases of primary tumoral hyperaldosteronism from 6 cases of adrenal hyperplasia.