The published studies on histological staging and response to steroid therapy of membranous glomerulonephritis are not consistent. We analysed data from 25 adult patients with stage I (group 1, n = 7) and stage II (group 2, n = 18) disease. The interval between clinical onset and admission was similar in the two groups. At admission all patients had normal creatinine clearance; proteinuria averaged 5.4 +/- 4.0 in group 1 and 9.0 +/- 4.0 in group 2 (g/day per 100 ml GFR). All patients received 6 months steroid therapy (months 1-2, 1 mg/kg b.w. per day; month 3-5: 0.65 mg/kg b.w. e.o.d.; month 6, tapering). After this cycle of steroid therapy, proteinuria declined by 84% in group 1 (five patients being in partial remission, i.e. 0.4-2 g/day, and two patients in complete remission, i.e. less than or equal to 0.3 g/day) and by 47% in group 2 (two patients being in complete remission and six in partial remission). Only 1 patient in group 1 relapsed with nephrotic proteinuria after 36 months, and renal function was still normal in all patients at the most recent follow-up (59 +/- 32 months). In contrast, 14 patients in group 2 had nephrotic syndrome and seven renal insufficiency at the most recent follow-up. We conclude that short-term steroid therapy is effective only in patients with early membranous changes.