Clinical trials have shown the beneficial effects of angiotensin-converting enzyme (ACE) inhibitors in delaying the progression of diabetic renal disease. There is less evidence from primary clinical trials of nondiabetic renal disease. We performed an updated meta-analysis to determine the efficacy of ACE inhibitors in slowing the progression of renal disease over a broad range of functional renal impairment. We included published and unpublished randomized, placebo-controlled, parallel trials with at least 1 year of follow-up available from January 1970 to June 1999. In nine trials of subjects with diabetic nephropathy and microalbuminuria, the relative risk for developing macroalbuminuria was 0.35 (95% confidence interval [CI], 0.24 to 0.53) for individuals treated with an ACE inhibitor compared with placebo. In seven trials of subjects with overt proteinuria and renal insufficiency from a variety of causes (30% diabetes, 70% nondiabetes), the relative risk for doubling of serum creatinine concentration or developing end-stage renal disease was 0.60 (95% CI, 0.49 to 0.73) for individuals treated with an ACE inhibitor compared with placebo. Treatment of individuals with chronic renal insufficiency with ACE inhibitors delays the progression of disease compared with placebo across a spectrum of disease causes and renal dysfunction.