Tissue regeneration by using stem/progenitor cells has been recognized as a maintenance or recovery system of many organs in adult. The isolation of endothelial progenitor cells (EPCs) derived from the peripheral blood (PB) was one of the amazing discovery for the recognition of "neovessel formation" in adult occurring as physiological and pathological responses. These findings that EPCs home to sites of neovascularization and differentiate into endothelial cells (ECs) in situ is consistent with "vasculogenesis", a critical paradigm well described for embryonic neovascularization, but proposed recently in adults in whom a reservoir of stem or progenitor cells contributes to vascular organogenesis. On the basis of the regenerative potency, these stem/progenitor cells are expected as a key factor of therapeutic applications for the ischemic diseases.