The pharmacokinetic properties and antihypertensive effects of cilazapril, a long-acting converting enzyme inhibitor, were investigated in seven hypertensive patients with renal failure. Cilazapril 1.25 mg was given orally once a day for 5 or 8 days. Cilazapril induced a significant decrease in both systolic and diastolic blood pressures, and its antihypertensive effect was still present 24 hours after administration. Serum-converting enzyme activity was markedly suppressed for at least 24 hours. No significant differences were noted in plasma peak level and the area under the curve between the first and last days of treatment. These results suggest that cilazapril has a long-lasting effect and is a useful antihypertensive agent in controlling blood pressure in hypertensive patients with renal failure.