The effect of hypotensive agents and of pressor substances on the rate of secretion of aldosterone was determined in normal subjects and in patients with hypertension or edema. The medullary hormones were studied because, in excess, they can produce hypertension in man. Angiotensin was studied because the major pathology of malignant hypertension is renal. The present work indicates that induced changes in the arterial blood pressure do not necessarily affect aldosterone secretion. The medullary hormones modified aldosterone output in a variable way, depending in part on the state of sodium balance. In contrast to the catecholamines, angiotensin consistently produced an increased secretion of aldosterone. The results suggest that aldosterone may regulate salt balance and blood pressure by its interaction with pressor substances such as angiotensin.