Peripheral artery disease (PAD) affects more than 8 million Americans. Although exercise, smoking cessation, anti-platelet therapy, cilostazol, statins and revascularization are used to treat PAD, men and women with PAD have significantly greater functional impairment and fasterfunctional decline than those without PAD. Stem and progenitor cell (PC) therapy that promotes neoangiogenesis is an emerging treatment modality in PAD. Progenitor cells, particularly those of endothelial origin, are involved in vascular repair and regeneration. They originate primarily but not exclusively from the bone marrow, differentiate into endothelial and other vascular cells, and contribute to neovascularization during tissue repair by direct and paracrine mechanisms. Endogenous, pharmacologically-stimulated, and exogenous PCs contribute to re-endothelialization and neovascularization. Granulocyte colony stimulating factor (G-CSF) and granulocyte-macrophage colony stimulating factor (GM-CSF) stimulate mobilization of hematopoietic and other PCs from the bone marrow.In the murine hind limb ischemia model, GM-CSF administered by injection or by plasmid transfer augments circulating levels of PCs, increases capillary density, and promotes arteriogenesis.GM-CSF also augments neo-endothelialization of denuded arteries, promotes proliferation, differentiation and survival of hematopoietic cells, monocytes and macrophages.