The localization of intrarenal cross-linked fibrin was examined by the effect of monochloroacetic acid treatment on the kidney sections. In acute glomerulonephritis or in mild diffuse or focal proliferative type of nephritis, cross-linked fibrin was observed mainly within glomerular capillary walls. Extension of cross-linked fibrin deposit over the mesangium or sclerotic area was seen in moderate to severe proliferative type of nephritis or in membranoproliferative glomerulonephritis. In hemolytic uremic syndrome or disseminated intravascular coagulation syndrome, cross-linked fibrin was detected within glomeruli and vessels.