The risk of severe hepatic damage in patients with chronic hepatitis B virus (HBV) infection is well known; more effective treatments for this infection are needed. Lamivudine is being studied in immunocompetent and immunosuppressed HBV infected patients. We report a patient suffering from chronic replicative HBV infection after allogeneic BMT, who responded to lamivudine therapy. A 24-year-old woman with CML received an allogeneic BMT from her HLA-identical sister in June 1992. Before transplant, her HBV status demonstrated viral contact without active infection (HBsAb+, HBcAb+ IgG, HBeAb+). Four months after BMT mild chronic liver GVHD appeared, requiring immunosuppressive treatment. Antibodies to HBV completely disappeared post-transplant. Acute icteric hepatitis occurred 2 years later, with HBsAg+, high level of HBV-DNA, HBeAg+ and HBcAb IgM+. Lamivudine 100 mg/day rapidly reduced transaminase levels and effected HBV-DNA disappearance within 2 months. The treatment was well tolerated; no hematological side-effects occurred. This preliminary observation warrants further investigation of lamivudine treatment in bone marrow transplanted patients with active HBV infection.