10 cases of aldosteronoma, 10 cases of pheochromocytoma and 10 cases of adrenocortical adenoma and hyperplasia were studied by using immunohistochemical staining for ET-1. All of the tumors were stained positivily for ET-1, ranging from weak diffuse (+) staining to moderate staining (++). In aldosteronomas ET-1 receptro may be down-regulated and ET-1 may play a paracrine role in regulating catecholamine in pheochromocytoma.