The angiotensin antagonist saralasin was given intravenously to six normotensive students before and after dietary sodium restriction and to two patients with renovascular hypertension. Both patients responded to the angiotensin antagonist with a decrease of the systolic (32 and 38 mm Hg) and of the diastolic (29 and 16 mm Hg) blood pressure. The small changes in blood pressure observed in the normotensive subjects during the infusion of the angiotensin antagonist indicate that angiotensin II plays no important role in the control of normal blood pressure in recumbent men. The fall in blood pressure induced by saralasin in both patients, however, demonstrates that their hypertension was at least partly angiotensin-dependent. Renal vein renin determination led to the same conclusions. The saralasin infusion test seems to be a simple procedure to diagnose angiotensin-dependent hypertension and will probably help to identify patients with suspected renovascular hypertension.