In order to study the influence of angiotensin converting enzyme (ACE) inhibition on the progression of chronic nephropathy, 70 patients with a median glomerular filtration rate (GFR) of 15 (range, 6 to 54) mL/min/1.73 m2 were randomized in an open study to basic treatment with enalapril or conventional antihypertensive treatment. The patients were followed for at least 2 years or until they needed dialysis. The groups were comparable with respect to age and sex distribution, etiology of renal diseases, initial levels of renal function and arterial blood pressure (BP), and protein intake. The therapeutic goal was a BP of 120 to 140/80 to 90 mm Hg. The GFR, estimated by the plasma clearance of 51Cr-EDTA, was measured every third month, and the individual rate of progression was calculated as the slope of the GFR v time plot. In the enalapril group, the median decline in GFR was -0.20 (range, +0.18 to -7.11) mL/min/1.73 m2/month and in the control group it was -0.31 (+0.01 to -1.97) mL/min/1.73 m2/month (P less than .05). There was no significant difference in blood pressure or plasma lipid levels between the groups. Thus, the progression of moderate to severe chronic nephropathy was slower on a basic treatment with enalapril as compared to conventional antihypertensive therapy.