BACKGROUND: S100 protein can promote axonal growth. Therefore, transplantation of induced bone marrow-derived mesenchymal stem cells (MSCs) that can secrete S100 may provide a beneficial microenvironment for neural regeneration. OBJECTIVE: To explore the changes in S100 expression during rat MSCs differentiation into Schwann cells in vitro. DESIGN, TIME AND SETTING: This cytology experiment was performed at the Jiangsu Key Laboratory of Neuroregeneration, Nantong University in China, from January 2006 to May 2007. MATERIALS: The rabbit anti-S100 polyclonal antibody was purchased from Dako, Denmark; the mouse anti-rat S100 monoclonal antibody was purchased from Sigma, USA. METHODS: MSCs were cultured from adult Sprague-Dawley rat femur and tibia. Cell proliferation was determined by the MTT method and CD markers, and cell cycle was meas-ured by flow cytometry. MSCs were induced to differentiate into SC cells. SC cells were stained for S100 protein, glial fibrillary acidic protein, and low-affinity nerve growth factor receptor. S100 protein and mRNA levels were evaluated by flow cytometry, Western blot, and reverse transcription-polymerase chain reaction. MAIN OUTCOME MEASURES: S100 protein and mRNA expression. RESULTS: MSCs exhibited high amplification potential over eight passages. Prior to induction, the majority of MSCs were at the G0/G1 phase of the cell cycle. After induction, MSCs displayed morphology changes similar to Schwann cells. Moreover, induction increased S100 mRNA levels. Immunofluorescence showed that MSCs expressed S100 protein, glial fibrillary acidic protein, and low-affinity nerve growth factor receptor at 7 days of induction. Induction also increased S100 protein levels compared with untreated MSCs. CONCLUSION: MSCs are capable of differentiating into Schwann cells-like cells under conditional induction in vitro, with increasing S100 mRNA and protein expression. Therefore, transplantation of induced bone marrow-derived mesenchymal stem cells (MSCs) that can secrete S100 may provide a beneficial microenvironment for neural regeneration. OBJECTIVE: To explore the changes in S100 expression during rat MSCs differentiation into Schwann cells in vitro. DESIGN, TIME AND SETTING: This cytology experiment was performed at the Jiangsu Key Laboratory of Neuroregeneration, Nantong University in China, from January 2006 to May 2007. MATERIALS: The rabbit anti-S100 polyclonal antibody was purchased from Dako , The mouse anti-rat S100 monoclonal antibody was purchased from Sigma, USA. METHODS: MSCs were cultured from adult Sprague-Dawley rat femur and tibia. Cell proliferation was determined by the MTT method and CD markers, and cell cycle was meas -ured by flow cytometry. MSCs were induced to differentiate into SC cells. SC cells were stained for S100 protein, glial fibrillary acidic protein, and l S100 protein and mRNA levels were evaluated by flow cytometry, Western blot, and reverse transcription-polymerase chain reaction. MAIN OUTCOME MEASURES: S100 protein and mRNA expression. RESULTS: MSCs exploring high amplification potential over eight passages . Prior to induction, the majority of MSCs were at the G0 / G1 phase of the cell cycle. After induction of S100 mRNA levels, MSCs displayed multivariate changes to Schwann cells. fibrillary acidic protein, and low-affinity nerve growth factor receptor at 7 days of induction. Induction also increased S100 protein levels compared with untreated MSCs. CONCLUSION: MSCs are capable of differentiating into Schwann cells-like cells under conditional induction in vitro, with increasing S100 mRNA and protein expression.