Effect of heparin and low-molecular-weight heparin (LMWH) were evaluated on 15 patients with proliferative glomerulonephritis with various degrees of sclerosing legion. Five cases were subcutaneously administered with 7000 to 11000 units of heparin for 4 weeks. Ten cases were administered with 60 unit/kg of LMWH by drip infusion for 4 weeks. Eleven cases were treated with prednisolone and all cases were treated with anti-platelet agent as well. Urinary protein excretion reduced from 3.0 +/- 1.8 to 1.8 +/- 0.6 g/day in the heparin-treated group and from 2.4 +/- 1.9 to 1.8 +/- 1.4 g/day in the LMWH-treated group, respectively. There were no remarkable changes in the renal functions of both groups. In one case, both heparin and LMWH brought about reduction of proteinuria. Therefore, LMWH reduced urinary protein excretion by the same mechanism as heparin. The LMWH has an advantage over heparin in that the former has less risk of causing bleeding. We conclude that heparin and LMWH reduce proteinuria in some patients with proliferative glomerulonephritis. The LMWH is beneficial in the treatment of proliferative glomerulonephritis with a sclerosing lesion.