OBJECTIVE: Recent advances in stem cell biology make it possible to induce the regeneration of injured axons and to replace lost cells in the injured spinal cord. It has been found that stem cells in human cord blood differentiate into mature neurons and glial cells both in vitro and in vivo. These findings suggest that human umbilical cord blood cells(HUCBs) can be used as therapeutic donor cells in cases of spinal cord injury. METHODS: To attempt the repair an injured cord following spinal cord injury(SCI), we transplanted HUCBs into contused spinal cords. This was found to promote a long-term improvement in neurologic function relative to a lesion-control group. HUCBs were cultured in vitro for 7 days. Bromodeoxyuridine(BrdU) was added to the media to allow the BrdU to integrate into dividing cells. Cultured HUCBs(2x106 cells) were then injected into the injury epicenter 7 days after SCI. The Basso-Beattie-Bresnahan(BBB) locomotor rating system was used to score functional improvement in HUCBs transplanted rats. Immunohistochemical staining for neurofilament, macrotubule associated protein 2(MAP-2), glial fibrillary acidic protein(GFAP), and nestin was performed. RESULTS: Immunohistochemical analysis 5 weeks after SCI showed that gliogenesis of the transplanted donor HUCBs had occurred within the adult rat spinal cord. These donor-derived astrocyte-like cells extended their processes into the host tissues and integrated well. HUCBs derived neurons(neurofilament, MAP-2) and nestin expressing cells were also detected. Behavior analysis using BBB rating scores showed that functional improvement was greater in transplanted rats than in non-treated rats. CONCLUSION: HUCBs are one of the potential sources for transplantation material for the treatment of SCI.