The renin-angiotensin system (RAS) is a coordinated hormonal cascade, the principal effector of which is angiotensin II (ANG II). All of the components of the RAS are present within the kidney and intrarenal formation of ANG II provides major regulation of renal hemodynamic and tubule function via a self-contained intrarenal RAS (3,4). We propose to study the interaction of the renal dopaminergic and renin-angiotensin systems in the regulation of Na+ balance and Na+ sensitivity of blood pressure (BP) and in the pathophysiology of essential hypertension in man.