Aim To explore the in vitro and in vivo angiogenic capacity and phenotypic properties about different clonal endothelial progenitor cell populations derived from human peripheral circulating blood. Methods Mononuclear cells were isolated by density-gradient centrifugation and incubated onto fibronectin-coated dishes in endothelial medium in the presence of vascular endothelial growth factor.The number of early clones was counted at 7 days and cells from another aliquot were cultivated continually until the late clones generated.Flow cytometry analysis was used to evaluate cells surface antigen expression and von willebrand factor(vWF),the endothelial cells marker was detected by indirect fluorescence staining.The capacities of in vitro and in vivo vascular genesis were assessed by plating cells onto collagen gels and implanting the cellularized gel into nude mice. Results Early clones failed to form second clone and were devoid of the capacity of in vitro and in vivo vascular genesis.Furthermore,cells derived from the early clones expressed mainly CD14 and CD45.In contrast to early clones,the late clones emerged until 21 to 28 days after cultivation and exhibited typically endothelial cells properties.Remarkably,cells originated from late clones had the ability to form second endothelial clones after replanted and generated tube-like structures when seeded onto collagen gels or transplanted into nude mice.In addition to the clearly morphological and functional differences,cells derived from late clones expressed obviously increased CD146(P<0.01) and reduced CD45 and CD14(P<0.001). Conclusions Under endothelial cultivating conditions,human peripheral blood mononuclear cells can generate early and late clones.Only cells originated from late clones exhibit double phenotypes of stem/progenitor and endothelial cells with the capacity of in vitro and in vivo vasculargenesis.