Introduction Selective homing of stem cells(SC) in the ischemic organ is a critical step in the therapeutic neovasculogenesis. We assessed the hypothesis that ICAM-1 might play a key role in selective homing of SC in the ischemic muscle and could be modulated by gene transfer to enhance homing of SC. Methods and results We examined the changes of cytokines and signal transduction in the ischemic muscle of mice that received unilateral femoral artery resection with ELISA and Western blot. VEGF and its down stream molecules were markedly elevated. The expression of adhesion molecules was assessed by immunofluorescent staining. Ischemia resulted in overexpression of ICAM-1 and LFA-1. But E-selectin was not expressed. Ligands on SC were identified by FACS and RT-PCR. ICAM-1 and its ligand, LFA-1 were expressed on bone marrow cells. To evaluate the functional role of ICAM-1, we performed attachment assay in vitro and quantitated SC homing in the ischemic muscle of mice with or without ICAM-1 blocking antibody. We could quantitate SC by means of histologic evaluation after transplantation of DiI-labeled SC or Tc-99m radioactivity after transplantation of SC labeled with Tc-99m HMPAO. ICAM-1 blocking antibody significantly reduced attached cell number [177.5짹27.5 to 90.0짹25.0 (/mm2), n=8, p<0.001] in vitro and the ratio of the amount of SC homing in the ischemic limb to that in the contralateral limb (4.1짹1.2 to 2.4짹0.46, n=4, p=0.43 by histologic analysis and 3.45짹0.63 to 1.93짹0.56, n=4, p=0.02 by radioactivity). To induce homing of SC by ICAM-1 overexpression, we performed intramuscular VEGF or constitutively active Akt gene transfer in unilateral limb of normal mice and control vector in contralateral limb. These gene transfer induced homing of SC, significantly (the paired mean number of SC: 25.5짹7.0 vs. 5.5짹1.3 (/mm2) by VEGF, n=4, p=0.007; 20.3짹4.0 vs. 5.0짹2.1 by constitutively active Akt. In conclusion, ICAM-1 is overexpressed in the ischemic muscle by VEGF and its down stream molecules and plays an important role in the process of homing of SC. This molecule can be modulated by gene transfer that suggests a prospective way of therapeutic neovasculogenesis by enhancing homing of SC.