The therapeutic benefits and risks of short-term corticosteroid were investigated in 8 patients with membranous nephropathy and hepatitis B surface antigenaemia. Seven patients presented with nephrotic syndrome, and the remaining patient had significant proteinuria. Their liver function tests were normal on repeated examination. Their sera demonstrated the persistent presence of hepatitis B virus surface antigen and high titres of antibody to hepatitis B virus core antigen. Hepatitis B virus e antigens were present in the sera of 4 patients at initial presentation. Their clinical responses were compared with 7 similar patients previously treated with diuretic therapy alone and acting as historic controls. Short-term corticosteroid (6 months) with stepwise reduction resulted in an early regression of the nephrotic syndrome in 3 patients. Five patients had persistent but reduced proteinuria. Transient liver impairment was observed in 3 patients. Corticosteroid therapy induced transient viral replication with increased serum concentration of hepatitis B virus e antigen and hepatitis B virus DNA. Two of the 7 patients receiving diuretics developed spontaneous remission though apparently later than those receiving corticosteroid. Yet complications such as liver dysfunction and hypertension were not observed in the patients treated with diuretics. Our findings suggest that corticosteroid therapy could be harmful in membranous nephropathy related to hepatitis B surface antigenaemia, as activation of viral replication could occur with corticosteroid therapy.