Background Recent studies indicate that bone marrow-derived cells may significantly contribute to atherosclerosis,post-angioplasty restenosis and transplantation-associated vasculopathy.The responsible bone marrow (BM) cells and mechanisms regulating the mobilization of these cells are currently unclear.The purpose of this study was to investigate the expression of granulocyte colony-stimulating factor (G-CSF) on injured arteries and its effects on mesenchymal stem cells (MSCs) differentiation into vascular smooth muscle cells (VSMCs) in the process of vascular remodeling.Methods Balloon-mediated vascular injury was established in female rats (n=1O0) which received radioprotective whole female BM cells by tail vein injection and male MSCs through a tibial BM injection after lethal irradiation.The injured and contralateral carotid arteries were harvested at 3,7,14 and 28 days after treatment.Results Morphometric analysis indicated that intima to media area-ratio (I/M ratio) significantly increased at 28 days,0.899±-0.057 (P ＜0.01),compared with uninjured arteries.Combining fluorescence in situ hybridization (FISH) and immunohistochemical analysis showed that a significant number of the neointimal cells derived from MSCs,(45.2±8.5)％ at 28 days (P=0.01),compared with (23.5±6.3)％ at 14 days.G-CSF was induced in carotid arteries subject to balloon angioplasty (fold mRNA change=8.67±0.63 at three days,relative G-CSF protein=0.657±-0.011 at three days,P ＜0.01,respectively,compared with uninjured arteries).G-CSF was chemotactic for MSCs but did not affect the differentiation of MSCs into smooth-muscle-like cells.Conclusion Increased expression of G-CSF by injured arteries plays an essential role in contribution to recruitment and homing of MSCs to the site of the arterial lesion.