The pharmacokinetics and pharmacodynamics of benazepril, an angiotensin converting enzyme (ACE) inhibitor, were investigated after administration of a single oral 5-mg dose and 7 more doses on consecutive days to hypertensive patients with normal renal function (NRF) and those with impaired renal function (IRF). The antihypertensive effect of benazepril was observed as early as 30 min after a single dose, and those effects during consecutive dosing were also sustained for 24 h with a lesser diurnal variation in blood pressure (BP). The time to peak (Tmax) and the apparent elimination half-life (t1/2) for benazepril were 0.6-0.7 h and 0.4-0.8 h, respectively. Tmax for its diacid was 1.5-2.4 h in both groups. The area under the plasma concentration-time curve to 24 h (AUC0-24h) for the diacid was significantly greater in the IRF group than in the NRF group. After consecutive dosing of benazepril, AUC0-24h and plasma peak level (Cmax) were significantly increased in the IRF group. Serum ACE activity was markedly suppressed for 24 h after administration, and the inhibition was closely related to plasma diacid levels. A significant inverse correlation was observed between creatinine clearance and the AUC for the diacid. These results suggest that benazepril is rapidly bioactivated to diacid and exhibits rapid onset and long-lasting antihypertensive effects. Dosage reduction might be required to minimize unnecessary drug accumulation in patients with severe IRF.