Hypertension in patients on chronic hemodialysis is thought to be largely of two types--volume dependent or renin dependent. If renin-dependent hypertension is mediated by angiotensin II, then angiotensin II antagonism should lower blood pressure. To test this hypothesis, the angiotensin II antagonist saralasin was given to 15 hypertensive patients on chronic hemodialysis. Patients were separated into two groups by their blood pressure response. In responders blood pressure was 191/112 mm Hg and fell to 147/85 during saralasin administration (P less than 0.01). In contrast, nonresponders had blood pressures of 190/111 mm Hg before and 188/110 during saralasin administration. Five responders subsequently ahd nephrectomies with normalization of their blood pressures. Plasma renin activity averaged 70 ng/ml . 3 h of angiotensin I in responders and increased to 110 after saralasin (P less than 0.05), while nonresponders had values of 21 before and after saralasin. These results offer strong support for the hypothesis that renin-dependent hypertension is an important mechanism in certain patients on chronic hemodialysis and that such patients will respond to angiotensin II antagonism.