During a retrospective study of dense deposit disease, we observed in three patients, unusual granular electron-dense deposits in the glomerular basement membrane in a laminar pattern. However, the distribution of these electron-dense deposits was similar to the distribution of the homogeneous, extremely electron-dense deposits of dense deposit disease. By light microscopy a membranoproliferative glomerulonephritis was demonstrated in two patients. The other patient had multiple myeloma with glomerulopathy and intratubular protein casts with histiocytic giant cell reaction. By immunofluorescence microscopy the presence of granular deposits in the glomerular basement membrane and mesangium was revealed in only one patient, with anti-human IgM and complement (C3). By electron microscopy was demonstrated the thickening of the glomerular basement membrane by densely packed small granular aggregates of varying sizes, ranging from 100 to 800 A in diameter. Similar electron-dense deposits in a laminar pattern were present in the Bowman's capsule and renal tubular basement membrane of two patients. The specific nature of these small electron-dense deposits is unknown.