We studied the effects of symptomatic, antiproteinuric treatment with NSAID's (n = 28) and ACE-inhibitors (n = 14) in patients with proteinuria due to idiopathic membranous glomerulopathy (MGP). These two treatment groups were compared with a group of patients who did not receive antiproteinuric medication (n = 14). Urinary protein loss was effectively lowered by NSAID and ACE inhibitor therapy from 9.5 +/- 1.0 to 4.5 +/- 0.5 g/day (mean +/- SEM) and from 9.8 +/- 1.4 to 3.9 +/- 0.7 g/day respectively, whereas the control group showed a slight fall in proteinuria from 6.9 +/- 0.8 to 5.5 +/- 0.8 g/day. As a result of this treatment hypoalbuminaemia and hypercholesterolaemia improved significantly: serum albumin rose in the NSAID group from 25.4 +/- 1.2 to 29.0 +/- 1.0, and in the ACEi group from 29.9 +/- 1.8 to 32.7 +/- 1.2 g/l (control group from 27.4 +/- 1.6 to 27.8 +/- 1.6 g/l, while cholesterol was lowered in the NSAID group from 8.5 +/- 0.5 to 7.5 +/- 0.4 and in the ACEi group from 8.7 +/- 0.5 to 7.6 +/- 0.4 mmol/l (control group from 9.7 +/- 1.1 to 8.5 +/- 1.0 mmol/l). The antiproteinuric effect of both drugs was well maintained during an 18-month follow-up. Progression towards end-stage renal failure was observed especially in patients with impaired renal function at entry. Remission of proteinuria occurred particularly in patients with lower baseline values of proteinuria, irrespective of the treatment modality.(ABSTRACT TRUNCATED AT 250 WORDS)