To investigate the beneficial effects of cilnidipine, a calcium channel blocker that shows high selectivity for N-type receptors, on the progression of chronic renal insufficiency, we compared the efficacy of cilnidipine to that of benazepril, an angiotensin-converting enzyme (ACE) inhibitor with known renal protective effects, in a one-year trial evaluating hypertensive control, serum creatinine, and albuminuria in a cohort of patients. Given the seeming importance of the etiology of chronic renal insufficiency in determining drug efficacy, we limited our study to 20 patients with a single common condition, benign nephrosclerosis. The average age of the patients was 62±4 yaers old. The changes in systolic and diastolic blood pressure over the course of the study year revealed a similar reduction with cilnidipine and benazepril. Both cilnidipine and benazepril induced similar reductions in systolic and diastolic blood pressure over the course of the study year. The baseline levels of serum creatinine were 1.40±0.2 mg/dl and urinary excretion of albumin was 168±10 mg daily. The levels of serum creatinine were not significantly changed throughout the study in either group, although the levels of urinary excretion of albumin were significantly decreased in both groups. There were no significant differences in either of these values between the two groups. In conclusion, both cilnidipine and benazepril equally and effectively reduced blood pressure and albuminuria in hypertensive patients with benign nephrosclerosis in a one-year trial. (Hypertens Res 2001; 24: 377-383)