Electron microscopic examination of renal biopsies from 19 patients with leprosy who had edema, proteinuria, or hematuria showed a proliferative glomerulonephritis in 12, amyloidosis in 2, and no lesion in 5. The proliferative glomerulonephritis was of different patterns: diffuse with or without exudation, focal, or mesangial. Subendothelial and/or subepithelial deposits were seen in five biopsies. Of the patients with glomerulonephritis, 3 had a reduced total serum complement level, 5 had erythema nodosum leprosum, 5 had evidence of recent streptococcal infection, and 2 had microfilariae in the peripheral blood. The significance of these findings is discussed.