Light microscopic and electron microscopic observations were performed on the kidney of patients with lupus nephritis, membranous nephropathy, IgA-IgG nephropathy and chronic glomerulonephritis by means of the horseradish peroxidase labeled antibody method described by Nakane in order to demonstrate immunoglobulin directly in the tissue of the renal glomeruli. The following results were obtained. The light microscopic enzyme-labeled antibody method showed the same results as the immunofluorescent antibody method on the staining patterns and intensities. Electron microscopic observation demonstrated that fine, electrondense granules indicating the localization of IgG were present within many deposits in and around the glomerular basement membrane of the renal glomeruli of lupus nephritis and membranous nephropathy. It was presumed that these deposits were antigen-antibody complex.