Objective To evaluate the differences between fresh and cryopreserved human umbilical cord blood as well as the stem cell homing.Methods Fresh or cryopreserved human umbilical cord blood cells were injected into lethally irradiated BALB/C nu+ mice.The mice survival rates,the successful transplantation evidence and the migration phenomenon were observed.Results The survival rates of the fresh group and the cryopreserved group were much higher than the control group,but there was no difference between the former two groups.Evidence of human hematopoiesis were observed by means of PCR or FACS.However,the pattern of migration was different berween fresh and cryopreserved cord blood stem cells. Conclusion Human cord blood contains high hematopoietic potential stem cells to cross xenogenetic barriers and successfully engraft in mice.Cryopreservation can keep the hematopoietic potential of cord blood,but may influence the adhesion molecular of the stem cells and thus influence their homing behavior.