Circulating progenitor cells home to sites of postnatal neovascularization and differentiate into endothelial cells but questions remain regarding the source of these cells. Indeed, a recent study suggests that nonbone marrow-derived cells may be even more important than bone marrow-derived cells in the setting of transplant arteriosclerosis. Thus, we aimed to thoroughly investigate the contribution of nonbone marrow-derived progenitor cells for neovascularization. We exclusively identified nonbone marrow-derived progenitor cells by combining a parabiosis model with reverse bone marrow transplantation followed by hindlimb ischemia. In this model, nonbone marrow-derived circulating progenitor cells attributed for 74+/-13% of the circulating progenitor cells that incorporated into the ischemic hindlimb. Increasing evidence suggests that organs such as small intestine and liver contain a considerable number of tissue resident progenitor cells and, thus, represent putative sources for nonbone marrow-derived progenitors. To track organ-derived progenitors, we transplanted sex-mismatched small intestine or liver, respectively, into rats followed by induction of hindlimb ischemia. These experiments show that organ-derived progenitor cells are contributing to postnatal vasculogenesis (intestine: 4.7+/-3.7%; liver: 6.3+/-2.2%). Based on the subsequent observation that liver-derived nonhematopoietic c-kit(+)CD45(-) progenitors are mobilized on induction of hindlimb ischemia, we prospectively isolated and intravenously infused these progenitors from murine livers. The isolated cells demonstrated a marked capacity for enhancing neovascularization and restoring blood flow to the ischemic hindlimb (no cells: 26.4+/-4.8% of normal blood flow; c-kit(+)CD45(-) cells: 67.0+/-8.0% of normal flow; P<0.01). In conclusion, we find that nonbone marrow-derived c-kit(+)CD45(-) progenitors contribute to postnatal neovascularization to an extent that is similar to that of bone marrow-derived progenitor cells. Intestine and liver represent a rich source for mobilized tissue-residing progenitor cells.