Background : Therapeutic neovasculogenesis with stem cells has been evaluated explosively. Recent studies suggested that there were two types of angiogenic cells having different characteristics in peripheral blood and they might play different roles in neovasculogenesis. We called one type of cells as early EPC and the other as late EPC in accord with their sequential appearance during culture. We tested the possibility of synergistic effect of the two types of cells in in vitro condition and in vivo experiment. Methods and Results : [1] Isolation of two types of EPC : We isolated two types of angiogenic cells from peripheral mononuclear cells by ex vivo culture. We confirmed that these cells were endothelial lineage expressing CD31, KDR, Flt-1 and vWF. We evaluated the angiogenic function of these cells with zymography and RT-PCR to detect MMP-2 and MMP-9 and ELISA to quantitate the angiogenic cytokines. Late EPC proliferated more rapidly than early EPC whereas early EPC secreted larger amount of MMP-2, 9 and VEGF, IL-8. [2] Interaction of the two types of cells : We executed Matrigel assay with these two types of cells and confirmed that these cells together made capillary network harmoniously. Late EPC proliferated more rapidly in supernatant of early EPC than in basal medium which was demonstrated in WST-1 assay and Matrigel assay. [3] Synergistic effect of the two types of cells on neovasculogenesis in hindlimb ischemia: We injected early EPC only or mixture of early EPC and late EPC into ischemic hindlimb of nude mice. Laser Doppler perfusion analysis showed superior recovery of perfusion in mixed group (perfusion ratio at 21st day : 0.47짹0.07 in early EPC only group vs. 0.65짹0.09 in mixed group, n=15 respectively, p=0.018) and excellent limb salvage effect in mixed group (salvage/tip necrosis/autoamputation : 5/4/6 in early EPC group vs. 10/3/2 in mixed group. Conclusion: We showed that early EPC contributed to neovasculogenesis by means of secreting angiogenic cytokines and MMP-2, 9 and late EPC provided endothelial cell necessary for vessel by rapid proliferation. Mixed therapy with these two types of cells potentiated the effect of therapeutic neoangiogenesis.