The effect of enalapril on urinary protein excretion and renal function was studied in six paediatric patients with various renal diseases causing nephroticrange proteinuria. In three younger children (aged 7-9 years) with steroid-resistant nephrotic syndrome, enalapril at a dose of 0.5 mg/kg per day given for 24 months yielded a temporary reduction of proteinuria in one child, a moderate and steady decrease in another and a complete disappearance of proteinuria in the third. Three adolescents, aged 17 years, took enalapril for 24 months at a dose of 20 mg/day. We observed no effect on proteiuria in one patient with Alport syndrome, a complete disappearance of urinary protein in one patient with membranoproliferative glomerulonephritis and a moderate decrease in the third patient who had idiopathic steroid-resistant nephrotic syndrome. Enalapril therapy resulted in an important reduction of proteinuria in two patients and a moderate decrease in three others. However this therapy was accompanied by a fall in glomerular filtration in all subjects, which was very marked in two patients. This fall in glomerular filtration may, however, simply reflect the natural course of the disease.