To evaluate the clinical features, immunopathology and the prognosis of hepatitis B virus-associated membranous nephropathy (HBVMN), 34 patients (25 boys and 9 girls) from April 1981 to November 1986 were studied. With Fab fragments of monoclonal antibodies, hepatitis B e antigen (HBeAg) was detected in the glomerular deposits from 30 cases (88.2%) and in the sera from 32 cases (94.1%). These results suggest that HBe Ag plays an important role in the development of HBVMN. In patients without corticosteroid treatment, HBV DNA was found as only episomal molecules with 3.2 kb in macrophage, T and B cells. The HBV cellular DNA disappeared within 12 months. In a HBVMN patient with corticosteroid treatment, even three years later, cellular HBV DNA was still detectable in T cells. They also had occasional proteinuria. From the in vitro study, we also demonstrated that corticosteroid stimulated endogenous HBsAg and HBeAg production from patient's mononuclear cells. Therefore, the use of corticosteroid could lead to a potential risk of enhancing viral replication. In addition, clinical trials of 32 cases demonstrate a relatively poor response to the steroid therapy with persistent heavy proteinuria (32.4%) or a high frequent relapse rate (38.2%); only one case (3.1%) had early response. Four cases received follow-up renal biopsy, progressive sclerosis with interstitial fibrosis being noted in each instance. The stage of membranous nephropathy in light microscope had progressed from stage I or II into III. One had impaired renal function. Therefore, HBVMN does not always take a benign course. Usage of corticosteroid in HBVMN patients should be avoided.