A protective effect of angiotensin-converting enzyme (ACE) inhibitors has been shown in patients with diabetic nephropathy but has not been clearly established in nondiabetic renal disease. A multicenter European study was designed to determine whether the ACE inhibitor benazepril was safe and effective in protecting residual renal function in patients with various renal diseases and mild to moderate renal failure. The trial involved 583 patients from 49 centers in Italy, France, and Germany. The patients were randomized to receive benazepril or placebo plus other antihypertensive agents, the target being a diastolic blood pressure of less than 90 mm Hg. Thirty-one patients in the benazepril group and 57 patients in the placebo group reached the end point [the time elapsed from entry to (a) doubling of serum creatinine (SCr) concentrations and (b) start of renal replacement therapy; p< 0.001 at 3 years]. The associated reduction in the relative risk of reaching the end point was 53% in benazepril-treated patients, with actuarial renal survival probability significantly better at 3 years. The best survival of renal function was observed in patients with chronic glomerular diseases and proteinuria greater than 1.0 g/24 h. Benazepril is effective in slowing the rate of progression and improving the survival of renal function in patients with renal diseases of various origins. This protective effect is associated with a clinically relevant decrease in both blood pressure and proteinuria.