Adenovirus-mediated VEGF gene delivery is being evaluated in clinical trials as a treatment for patients with vascular diseases that stem from ischemia, such as diffuse coronary artery disease and peripheral vascular disease. Although adenoviral vectors are one of the most widely utilized vectors to deliver therapeutic genes to cells, they also have a major limitation in that their inherent immunogenicity leads to the production of neutralizing antibodies that block effective repeat administration. Although this may be true of intravenous, intranasal, and other routes of administration, recent studies have indicated that it may be possible to effectively readminister adenovirus to skeletal muscle. The present study found improved efficacy after administration of AdVEGF(121.10), an E1/E3-deleted adenovirus encoding human VEGF(121) under the control of a CMV promoter in a rat hindlimb ischemia model. As expected, repeat administration of adenovirus resulted in a marked increase of circulating neutralizing antibody, yet nanogram quantities of VEGF protein were still detectable within the hindlimb skeletal muscle after a second administration of vector. The amount of VEGF protein produced after repeat administration translated into improved efficacy as evidenced by increased blood flow as measured by laser Doppler, increased vessel number upon post-mortem angiography, and an increased number of CD31-positive vessels. These findings have important implications for increasing the efficacy of adenovirus-mediated gene therapy in the treatment of peripheral vascular disease and coronary artery disease.