Preliminary results of the efficacy of high-dose intravenous human IgG in patients with biopsy-confirmed idiopathic membranous nephropathy (IMGN) were reported. Five patients with normal renal function (creatinine clearance 125.2 +/- 16 ml/min/1.73 m2 BSA) (Group A) and 4 patients with moderate renal insufficiency (creatinine clearance 65.5 +/- 8.3 ml/min/1.73 m2 BSA) (Group B) received pulse doses of IgG (0.4 g/kg BW) for 3 consecutive days; these 3-day boli were repeated 3 times at 21-day intervals; since then for a 10-month period one bolus once every 3 weeks has been administered. Five responder patients at the end of the trial received a new renal biopsy. In 4 Group A patients complete remission of proteinuria (daily proteinuria less than 0.2 g) was observed, whereas 1 patient showed partial remission (proteinuria 2 g/day). In Group B patients, 1 showed complete remission and 2 partial remission; in 1 patient no variation of proteinuria was noted. In responder patients clinical and biological findings of the nephrotic syndrome disappeared and a statistically significant increase of creatinine clearance was observed. In control biopsies at the end of the trial the immunofluorescence staining failed to find immunodeposits and recovery of glomerular lesions at light microscopy. In conclusion, IgG therapy seems to be of benefit to patients with IMGN but a randomized clinical trial to confirm this preliminary report is needed.