Hepatitis B virus (HBV) reinfection after liver transplantation is a major problem. HBV is mainly a hepatotrophic virus but replicates in many extrahepatic tissues. We present here two cases of infected patients who underwent liver transplantation. Both underwent bone marrow (BM) and liver biopsies after transplantation. Biopsy specimens were stained for hepatitis B surface antigen (HBsAg), and bone marrow aspirates and were separated for all subsets of cells. In both cases, HBV DNA analysis detected DNA in all BM fractions after transplantation, but HBV recurrence was found only in one case. We suggest that graft reinfection after liver transplantation may be caused by active replication of HBV in extrahepatic tissues and that BM cells are probably one of the major sanctuaries. The use of immunoprophylaxis based on BM-HBV studies is discussed. Copyright © 1996 by the American Association for the Study of Liver Diseases.