Angiopoietin1 (Ang1) is a vascular growth factor, essential for normal vascular development. Its role in adult physiological and pathological angiogenesis is not yet clear and a detailed investigation into its angiogenic phenotype (e.g. sprouting, intussuscepption, arteriogenesis, pericyte recruitment, etc) is lacking. To characterise Ang1 mediated angiogenesis in more detail, an adenoviral mesenteric angiogenesis assay was used (Wang et al. 2004) Male Wistar rats (300g) were anaesthetised by halothane inhalation and a laparotomy performed. All animals were killed humanely. A region of the mesentery was externalised and a mesenteric panel draped over a quartz pillar. The vasculature was imaged and 25μl of Ad–growth factor was injected into the fat pad. The panel was marked with 0.6% Monastral blue in mammalian Ringer solution, the gut replaced in the animal and the animal allowed to recover. 6 days later the same panel was found, imaged as before, and fixed in vivo with 4% paraformalydehyde. The panel was then prepared for immunofluorescent staining, before being imaged with confocal microscopy. 5 images per panel were taken, and measurements of vessel density, branch point density, sprout density, vessel diameter, length, endothelial cell proliferation pericyte coverage. N=5 in all groups. All analyses were carried out by Student’s t test or ANOVA as appropriate. Ad–eGFP elicited no angiogenic response, whereas Ad–VEGF and Ad–Ang1 increased the angiogenic index. As previously demonstrated in the mesentery Ad–VEGF induced a ‘sprouting angiogenesis ’ phenotype, Ang1 displayed a significantly lower vessel density, reduced sprout density, branch point density than Ad–VEGF. However vessels were longer and wider) in the Ang1 compared with the VEGF injected mesenteries. Taken together these results show that the increase in Angiogenic index induced by Ang1 could be attributed to fewer, larger vessels compared with that induced by VEGF.