Nitric oxide (NO) synthase (eNOS) modulates angiogenesis in response to tissue ischemia. The study tested the hypothesis that eNOS is a downstream mediator of in vivo angiogenesis. In two animal models, rabbits and mice, with operatively induced hindlimb ischemia, eNOS was found to be critical for angiogenesis. In rabbits, dietary supplementation with L-arginine, which increases endogenous NO production, significantly improved angiogenesis, as evidenced by increased capillary density, improved vascular reactivity, and enhanced perfusion. In mice, eNOS knockout (eNOS^-/-) mice showed impaired angiogenesis, which was not improved by VEGF administration, suggesting that eNOS acts downstream of VEGF. These findings indicate that defective endothelial NO synthesis may limit angiogenesis in patients with endothelial dysfunction related to atherosclerosis, and that oral L-arginine supplementation could be a potential therapeutic strategy for accelerating angiogenesis in patients with advanced vascular obstruction. The study also demonstrated that eNOS is essential for angiogenesis in ischemic tissues in vivo, and that exogenous NO donors failed to restore angiogenesis in eNOS^-/- mice. The results suggest that eNOS is a critical regulator of angiogenesis, and that dietary L-arginine supplementation enhances endogenous NO production, thereby promoting angiogenesis.Nitric oxide (NO) synthase (eNOS) modulates angiogenesis in response to tissue ischemia. The study tested the hypothesis that eNOS is a downstream mediator of in vivo angiogenesis. In two animal models, rabbits and mice, with operatively induced hindlimb ischemia, eNOS was found to be critical for angiogenesis. In rabbits, dietary supplementation with L-arginine, which increases endogenous NO production, significantly improved angiogenesis, as evidenced by increased capillary density, improved vascular reactivity, and enhanced perfusion. In mice, eNOS knockout (eNOS^-/-) mice showed impaired angiogenesis, which was not improved by VEGF administration, suggesting that eNOS acts downstream of VEGF. These findings indicate that defective endothelial NO synthesis may limit angiogenesis in patients with endothelial dysfunction related to atherosclerosis, and that oral L-arginine supplementation could be a potential therapeutic strategy for accelerating angiogenesis in patients with advanced vascular obstruction. The study also demonstrated that eNOS is essential for angiogenesis in ischemic tissues in vivo, and that exogenous NO donors failed to restore angiogenesis in eNOS^-/- mice. The results suggest that eNOS is a critical regulator of angiogenesis, and that dietary L-arginine supplementation enhances endogenous NO production, thereby promoting angiogenesis.