We studied the efficacy of captopril, an angiotensin-converting enzyme inhibitor in treating persistent moderate or severe proteinuria in children with various glomerular diseases other than minimal-change nephrotic syndrome. Captopril was administered for 3 months to 15 normotensive and nonazotemic or mildly azotemic patients (12 boys, 3 girls) in whom corticosteroid and cytotoxic treatment had failed to induce remission. Urinary protein excretion decreased from 2873.14 +/- 1937.50 (mean +/- s.e.m.) to 1684.71 +/- 1463.13 mg/day (P < 0.05). The reduction in proteinuria was not related to a significant fall in systemic blood pressure or a change in renal function. Serum albumin did not rise and side effects due to captopril were not observed. We concluded that, in the short term, captopril can be used safely and effectively for decreasing the proteinuria of nephrotic children unresponsive to conventional therapy.