The antihypertensive effects and pharmacokinetic properties of lisinopril, an angiotensin-converting enzyme (ACE) inhibitor, were investigated in hypertensive patients with normal renal function (NRF, mean serum creatinine 1.0 mg/dl, n = 9) and those with impaired renal function (IRF, mean serum creatinine 1.7 mg/dl, n = 8). Lisinopril was administered orally (10-mg dose once daily for 5 or 8 days). Measurement of blood pressure (BP) and sampling of blood specimens were made on the first and last days of treatment. During consecutive dosing of lisinopril, its antihypertensive effects were sustained for greater than or equal to 12 h with less diurnal variation of BP. Serum ACE activity was markedly suppressed for 24 h. Plasma levels of lisinopril in the IRF group were higher than those in NRF with significant differences in the peak levels and areas under the plasma concentration time curve (AUC). A significant inverse correlation was found between the creatinine clearance and the AUC for lisinopril. These results suggest that lisinopril has a long-lasting action and that it is a useful antihypertensive agent for controlling BP in patients with either NRF or mild IRF. When administered for an extended period, however, more careful consideration should be given to the dose in patients with IRF than in patients with NRF to minimize the possibility of untoward side effects.