Stem cell-based therapy has received attention as a possible alternative to organ transplantation, owing to the ability of stem cells to repopulate and differentiate at the engrafted site. We transplanted bone marrow-derived mesenchymal stem cells (BMSCs) into liver-injured rats to test the therapeutic effect. Rat bone marrow cells were cultured in the presence of hepatocyte growth factor (HGF). RT-PCR and immunocytochemical analysis indicated that the BMSCs expressed the albumin mRNA and the production of protein after cultivation with HGF for 2 weeks. The BMSCs appeared to differentiate into hepatocyte-like cells in response to the culture with HGF. After labeling with a fluorescent marker, the BMSCs were transplanted into CCl(4)-injured rats by injection through the caudal vein. The liver was excised and blood samples were collected 4 weeks later. Engraftment of the transplanted BMSCs was seen with significant fluorescence in the injured liver. Transplantation of the BMSCs into liver-injured rats restored their serum albumin level and suppressed transaminase activity and liver fibrosis. Therefore, BMSCs were shown to have a therapeutic effect on liver injury. Recently, we have been trying to use mesenchymal stem cells isolated from dental papilla of discarded human wisdom teeth. Autologous transplantation of mesenchymal stem cells from bone marrow and dental papilla could be ethically and functionally promising for stem cell-based therapy.