Recent studies have shown the potential of olfactory ensheathing cells (OECs) for treating spinal cord injuries. For clinical application it is important to understand the behavior of these cells with the normal and injured cord environment. In this study, we compared migration of rat and human OECs in normal and immuno-deficit (nude) rats, after transplantation into the grey matter. OECs were obtained from nasal mucosa of donor SD rats or by biopsy from human volunteers. The purified OECs (>99%) were pre-labeled with CFDA-SE (Molecular Probes), injected into the spinal cord at T10 (0.8mm lateral, 1mm deep), then animals were sacrificed at 4, 24 hours, and 7 days post-transplantation. Within 4 hours of transplantation, both human and rat OECs had started migrating in SD and nude hosts, with bipolar cells extending into host tissue at the egdes of the transplantation site. However, death of human OECs was obvious in SD hosts by 24 hours. At 24 hours in nude hosts, rat and human cells had migrated up to 270孠transversely (medially and laterally) and up to 450孠longitudinally (rostrally and caudally). By 7 days, OECs extended 200-700孠from the injection site in transverse directions compared with 700-1000 孠longitudinally. Migration was also assessed in injured cord, by a hemisection of the nude cord 5mm rostral or caudal to the transplantation site, at the time of OEC injection. After 7 days, macrophages were numerous both around the injury and at the transplantation site; OEC survival was less and longitudinal migration was reduced. The results suggest that rat and human OECs have similar ability to migrate within the cord. However, concomitant injury at the time of transplantation leads to reduced survival and impaired migration. This study was funded by NH&MRC, Australia.