Vascular endothelial growth factor (VEGF), a potent mediator of angiogenesis, has been used in gene transfer experiments to enhance blood flow to ischemic tissues. A major source of endogenous VEGF is the platelet, a blood element known to contain substantial reserves of VEGF. In this study we evaluated the hypothesis that gene transfer of thrombopoietin (TPO; the systemic signal for megakaryocyte differentiation) is angiogenic due to an increase in the level of platelets which provide a source of VEGF that mediates local angiogenesis. The impact of quadriceps administration of AdmTPO (E1−E3− adenovirus vector expressing the murine TPO cDNA behind a CMV promoter), on recovery of ischemic hind limb blood flow in mice following excision of a section of external iliac artery was assessed by Doppler scanning. On day 28 after ligation, blood flow to the treated limb, expressed as the flow ratio between the ischemic and control limb, recovered to 0.38 ± 0.10 for the control group treated with 108 particle units (pu) of AdNull (identical to AdmTPO but with no transgene) while treatment with 108 pu of AdmTPO mediated recovery to a flow ratio of 0.83 ± 0.06. (p 0.08). These results suggest that TPO can induce angiogenesis by elevating platelet levels that act as a local source of VEGF and suggests possible roles of thrombopoietic factors in angiogenic therapy.