The possibility has been explored of using a specific angiotensin ii antagonist, saralasin (P-113, 1-sar-8-ala-angiotensin ii) to recognize patients whose hypertension depends upon excessive angiotensin ii activity. Among 60 hypertensive patients, saralasin infusion reduced blood pressure in 16 "responders," but not in 44 "nonresponders." The "responders" had the following findings: elevated plasma renin activity in renal vein (or veins) or peripheral veins or both (16 of 16); reduced renal blood flow, shown by arteriography, isotopic studies or pyelography (15 or 16), or progressive azotemia (one of 16); and reduction in blood. These findings indicated that angiotensin ii probably caused hypertension in the "responders," One "nonresponder" had renal vein levels of plasma renin activity suggestive of angiotensinogenic hypertension. Since hypertension was invariably angiotensinogenic when it was reduced by saralasin and, with one possible exception, was never angiotensinogenic in "nonresponders," the antagonist appears to provide an efpressure to or toward normal after corrective operation (four of four) or propranolol therapy (eight of eight). fective means of recognizing angiotensinogenic hypertension.