This is the first report of primary glomerular disease with both mesangial IgA and subepithelial IgG deposits in the glomeruli at the same time. This nephropathy, discovered in 3 patients, is either a new disease entity or an overlapping of IgA nephropathy and membranous nephropathy. Follow-up studies may clarify the pathogenesis of IgA nephropathy and/or membranous nephropathy. In 1 patient the clinical findings resembled those of IgA nephropathy, and in the other 2 they were those of membranous nephropathy. Light microscopy showed generalized diffuse increases in mesangial cells and matrix, and there was slight capillary wall thickening. In the glomeruli, immunofluorescence microscopy demonstrated both granular deposits of IgA in the mesangium and granular deposits of IgG along the capillary loops. On electron microscopy, electron-dense deposits were identified not only in the mesangium but also on the epithelial side of the glomerular basement membrane. These findings were confirmed by the immunoperoxidase technique in electron-microscopic studies of these antibody classes. These glomeruli contained both the dense reaction products of IgA deposits in the paramesangium and mesangial matrix and the dense reaction products of IgG deposits on the epithelial side of the basement membrane.