Aim To investigate the impact by delivery of different number of endothelial progenitor cells(EPC)on repair of injured vessels.Methods Mononuclear cells(MNC)were isolated from rabbit peripheral blood by density-gradient centrifugation.MNC were cultured in endothelial growth medium for 7 days,yielding EPC.Autologous EPC(5×105 cells or 2×105 cells in 100 μL saline)or 100 μL saline alone(control)were administered into a rabbit model of balloon carotid injury.Meanwhile the cells were labeled by CM-DiI for cells tracking.Four weeks after transplantation,rabbits were killed.Fluorescence-labeled EPC,endothelial regeneration rate and interal area/media area(IA/MA)ratio were detected.Results Four weeks after transplantation,fluorescence-labeled EPC were detected within the media,neointima and on the luminal surface of injured vessel.Local transplantation of EPC compared with saline administration markedly accelerated endothelialization of denuded vessel,especially in the group of 5×105 EPC.Meanwhile EPC treatment significantly reduced neointimal formation.Conclusions Delivery of EPC to balloon-injured arteries is associated with accelerated reendothelialization and reduced neointimal formation.More notable effect may turn out when larger number of EPC are deliverd.