In addition to its role in hematopoiesis, bone marrow appears to be a reservoir of stem cells that can differentiate into components of vessel wall. Upon stimulation by factors such as tissue ischemia, bone marrow stem cells can enter into circulating blood, and incorporate into areas of vascular development. Animal models suggest that bone marrow is a cellular source for tissue repair and/or regeneration. Data from humans, and clinical trials using bone marrow stem cells for the treatment of chronic ischemia in limbs and myocardium, support the view that stem cells may represent a new tool for the treatment of ischemia.