AIM: To investigate the differentiation of rat bone marrow stem cells in liver after partial hepatectomy. METHODS: Bone marrow cells were collected from the tibia of rat with partial hepatectomy, the medial and left hepatic lobes were excised. The bone marrow stem cells (Thy(+)CD3(-)CD45RA(-) cells) were enriched from the bone marrow cells by depleting red cells and fluorescence-activated cell sorting. The sorted bone marrow stem cells were labeled by PKH26-GL in vitro and autotransplanted by portal vein injection. After 2 wk, the transplanted bone marrow stem cells in liver were examined by the immunohistochemistry of albumin (hepatocyte-specific marker). RESULTS: The bone marrow stem cells (Thy(+)CD3(-)CD45RA(-): cells) accounted for 2.8% of bone marrow cells without red cells. The labeling rate of 10 mu M PKH26-GL on sorted bone marrow stem cells was about 95%. There were sporadic PKH26-GL-labeled cells among hepatocytes in liver tissue section, and some of the cells expressed albumin. CONCLUSION: Rat bone marrow stem cells can differentiate into hepatocytes in regenerative environment and may participate in liver regeneration after partial hepatectomy. (C) 2006 The WJG Press. All rights reserved.