Two adult cases of membranoproliferative glomerulonephritis (MPGN) associated with chronic hepatitis B were reported. Serum HBsAg, HBeAg and anti-HBc were positive. Glomerular changes were essentially the same in both patients and consistent with MPGN type III. Immunofluorescence microscopy revealed diffuse granular and lumpy deposits of IgG, IgA, IgM, C1q and C3 along glomerular capillary walls and in mesangial areas. Granular deposition of HBsAg was observed along capillary walls and in mesangial areas, and the staining patterns were similar to those of immunoglobulins and complements in both patients. Glomerular deposition of HBeAg, however, was negative in one case, and only slight and segmental in the other case. These findings suggest that HBsAg rather than HBeAg may play a role in the pathogenesis of MPGN associated with hepatitis B virus infection in adults.