Recent experimental and clinical data have suggested that angiotension converting enzyme (ACE) inhibitors may decrease glomerular proteinuria by specific effects on the glomerulus. We studied a group of 15 adult patients with chronic renal failure and proteinuria due to various glomerulopathies. These patients had mild to moderate hypertension which was effectively controlled with conventional antihypertensive therapy. We then treated the patients with captopril, maintaining a similar dietary protein and salt intake. After 6 months of study, proteinuria was reduced significantly without reduction in inulin or para-aminohippurate clearance. This supports the concept that captopril may have salutary effects on the glomerulus, independently of its effect on systemic blood pressure.