Bone marrow stem cells develop into hematopoietic and mesenchymal Lineages but have not been known to participate in production of hepatocytes, biliary : cells, or oval cells during Liver regeneration. Cross-sex or cross-strain bone marrow and whole Liver transplantation Were used to trace the origin of the repopulating Liver cells. Transplanted rats were treated with 2-acetylaminofluorene, to block hepatocyte proliferation, and then hepatic injury, to induce oval cell proliferation. Markers for Y chromosome, dipeptidyl peptidase IV enzyme, and L21-6 antigen were used to identify Liver cells of bone marrow origin. From these cells, a proportion of the regenerated hepatic cells were shown to be, donor-derived. Thus, a stem cell associated with the bone marrow has epithelial cell Lineage capability.