Background Despite major advances in both surgical and percutaneous revascularization techniques, limb salvage and relief of ischemic pain cannot be achieved in many patients with diffuse peripheral vascular disease.Vascular endothelial growth factor (VEGF) is a heparin-binding, endothelial cell-specific mitogen. Previous studies have suggested that VEGF is a regulator of naturally occurring physiological and pathological angiogenesis. In this study, the therapeutic potential of intramuscularly administered VEGF was investigated in a rabbit model of chronic hindlimb ischemia.Methods and Results Ischemia was induced in the hindlimb of 24 New Zealand White rabbits by ligation of the distal external iliac artery and complete excision of the femoral artery.Ten days after the induction of limb ischemia (day 0), saline (group A, n=7) or the 165-amino acid isoform of recombinant human VEGF (group B: 200 micrograms, n=6; group C: 500 micrograms, n=7; group D: 1000 micrograms, n=4) was administered intramuscularly into the ischemic limb daily for 10 days. Angiography on day 30 after initiation of therapy revealed statistically significant dose-dependent augmentation of collateral vessels in the ischemic limb (angiographic score: group A, 13.0+-1.1; group B, 21.2+-1.8; group C, 27.3+-1.4; group D, 31.5+-2.5). Capillary density in the thigh muscles on day 30 was 1.6 times greater in VEGF groups versus controls (176+-15.3 versus 113+-27.3 per square millimeter, P<.05). Amelioration of the hemodynamic deficit in the ischemic limb was documented by calf systolic blood pressure ratio (group A, 0.52+-0.02; group B, 0.67+-0.02; group C, 0.73+-0.01; group D, 0.82+-0.03). "Clinical" improvement (incidence of calf muscle atrophy and distal limb necrosis: group A, 85.7%; group B, 33.3%; group C, 14.3%; group D, 0%) was greater in VEGF- treated than in control animals, again in a dose-dependent fashion.Conclusions These findings demonstrate a significant dose-dependent augmentation in limb perfusion accompanied by evidence of increased collateral formation after intramuscular administration of VEGF in ischemic rabbit hindlimbs. This study thus supports the hypothesis that administration of VEGF to stimulate angiogenesis may represent a new therapeutic modality in the management of arterial insufficiency. (Circulation. 1994;90(part 2):II-228-II-234.)