Vascular endothelial growth factor (VEGF) is a potent endothelial cell mitogen and morphogen, which stimulates angiogenesis in a wide variety of tissues and lesions in vivo. In this study, we applied adenoviral vector delivered human VEGF165 cDNA to develop focal non-tumor angiogenesis in the mature mouse brain. Seventy-two adult CD-1 mice underwent Ad h VEGF, Ad lacZ, and saline injection for up to fourweeks. An adenoviral suspension containing 1 x 10(9) particles was injected stereotactically into the right hemisphere of the brain. The results showed that VEGF expression was increased in the Ad h VEGF transduced mice compared to Ad lacZ or saline injected mice ( P < 0.05). VEGF-positive cells were mainly located in the injection hemisphere of Ad h VEGF transduced mice. Quantitative vessel counting showed that microvessels in the Ad h VEGF transduced mice increased following 2 weeks of Ad h VEGF gene transfer compared to the other two groups (Ad h VEGF:241 +/- 19 vs. Ad lacZ :148 +/- 17 and Saline:150 +/- 14 vessels/mm2, P < 0.05). Morphology showed typical angiogenic changes. PCNA-positive staining confirmed these microvessels were actively proliferating. Our study demonstrates that Ad h VEGF-induced VEGF hyper-stimulation causes focal angiogenesis in the mature mouse brain. This novel method of inducing in vivo brain focal angiogenesis provides an opportunity to study the molecular mechanisms independent of the confounding effects of upstream inciting stimuli such as ischemia or tumor.