The therapeutic effect of corticosteroid in hepatitis B virus (HBV) related membranous nephropathy was investigated in a 29-year-old chronic HBV carrier. Prednisolone (60 mg/day) was given for eight weeks and gradually reduced over the subsequent four months. In the renal biopsies taken before and after corticosteroid therapy, light microscopy revealed progression of sclerosis. Immunofluorescent staining showed glomerular capillary deposition of hepatitis B core antigen (HBcAg) by polyclonal antisera and hepatitis B e antigen (HBeAg) by monoclonal antibodies. Electron microscopy revealed 40-50 nm diameter virus-like particles in the glomeruli only from the biopsy performed after corticosteroid therapy. The serum concentrations of alanine aminotransferase, HBeAg, and HBV DNA increased with corticosteroid therapy suggesting active viral replication despite the absence of overt clinical hepatitis. Renal function did not improve and corticosteroid therapy was apparently not helpful in this patient. Our results conflict with the earlier notion that short-term corticosteroid does not interfere with a favorable outcome of the infection of the related renal disease.