Nitrendipine, a calcium entry blocker, was administered by gavage (3 mg/100 g body weight/day) to rats with prolonged angiotensin-II-(AII) induced hypertension. AII was infused by osmotic minipump implanted subcutaneously. Persistent hypertension was established after 5 days. Normotensive control rats had empty sham pumps. Nitrendipine, administered from day 11 to 15 after pump implantation, normalized blood pressure consistently in AII rats, whereas it had no significant hypotensive effect in controls. Renal clearance experiments in anesthetized rats revealed that nitrendipine reversed all noted abnormalities of AII-infused rats, including hypertension and reductions in glomerular filtration rate, renal blood flow, and urinary sodium excretion. When receiving nitrendipine, sham controls did not show significant changes in blood pressure, renal function, or natriuresis. The results demonstrate that oral administration of nitrendipine is highly effective in normalizing blood pressure during prolonged AII-induced hypertension. The antihypertensive effect is achieved by this calcium entry blocker's vasodilatory action, supported by a marked natriuretic effect. By contrast, blood pressure and renal function of normotensive control rats were not appreciably affected by oral nitrendipine.