BACKGROUND: It has been previously demonstrated that the neural cell microenvironment has the ability to induce differentiation of bone marrow mesenchymal stem cells (BMSCs) into the neural cells. OBJECTIVE: To establish a co-culture system of human BMSCs and neural cells, and to observe effects of this co-culture system on differentiation of human BMSCs into neural cells. DESIGN, TIME AND SETTING: A comparative observation experiment, performed at the Center Labora-tory of the Affiliated Hospital of Medical College Qingdao University from October 2006 to December 2007. MATERIALS: Neural cells were obtained from human fetal brain tissue. BMSCs were harvested from fe-male patients that underwent autonomous stem cell transplantation. METHODS: BMSCs in the co-culture group consisted of BMSCs and third passage neural cells. BMSCs in the control group were solely cultured in vitro. MAIN OUTCOME MEASURES: Morphological changes of BMSCs were observed, and expression of the neuronal specific marker, neuron-specific enolase (NSE), was analyzed by immunofluorescence staining after 4-5-day co-culture. RESULTS: The number of neural cells in the co-culture group increased and the cells spread on the culture bottle surface. Radial dendrite formed and connected with each other. NSE-immunoreactive cells were also detected. The positive ratio of NSE-positive cells reached (32.7±11.5)%, with morphological characteristics similar to neuronal cells. Human BMSCs did not express NSE in the control group. CONCLUSION: The microenvironment provided by neurons induced differentiation of BMSCs into neu-ronal-like cells. BACKGROUND: It has been previously previously that that neural cell microenvironment has the ability to induce differentiation of bone marrow mesenchymal stem cells (BMSCs) into the neural cells. OBJECTIVE: To establish a co-culture system of human BMSCs and neural cells, and to observe effects of this co-culture system on differentiation of human BMSCs into neural cells. DESIGN, TIME AND SETTING: A comparative observation experiment, performed at the Center Labora-tory of the Affiliated Hospital of Medical College Qingdao University from October 2006 to December 2007 MATERIALS: Neural cells were obtained from human fetal brain tissue. BMSCs were harvested from fe-male patients that underwent autonomous stem cell transplantation. METHODS: BMSCs in the co-culture group consisted of BMSCs and third passage neural cells. group were solely cultured in vitro. MAIN OUTCOME MEASURES: Morphological changes of BMSCs were observed, and expression of the neuronal specific m arker, neuron-specific enolase (NSE), was analyzed by immunofluorescence staining after 4-5 -day co-culture. RESULTS: The number of neural cells in the co-culture group increased and the cells spread on the culture bottle surface. Radial The positive ratio of NSE-positive cells reached (32.7 ± 11.5)%, with morphological similar similar to neuronal cells. Human BMSCs did not express NSE in the control group CONCLUSION: The microenvironment provided by neurons induced differentiation of BMSCs into neu-ronal-like cells.