The antiproteinuric efficacy of angiotensin-converting-enzyme inhibitors (ACEI) has been extensively investigated in patients with several types of nephropathy, but there are few data on the use of ACEI in patients with primary glomerular disease without renal function impairment. We evaluate the effect of long-term therapy with captopril on arterial pressure and proteinuria in 13 patients with primary glomerular disease, selected on the following criteria: persistent proteinuria greater than 600 mg/day, serum creatinine less than or equal to 1.5 mg/dl, no dietary restriction or antihypertensive or immunosuppressive therapy for at least 9 months prior to enrolment. Ten of 13 patients were normotensive. The treatment with captopril induced an early and persistent decrease in proteinuria (41%), and a significant increase in serum albumin. We did not find a significant correlation between changes in MAP and changes in protein loss or between variations in serum creatinine and in proteinuria. Our results demonstrate that captopril is effective in reducing proteinuria in patients with primary glomerular disease with normal renal function. Since the antiproteinuric effect is not associated to a concomitant decrease in arterial pressure, we presume that it might be due to a specific intrarenal action of captopril.