There is increasing interest in whether incretin based medications have favourable vascular actions, including improving endothelial function and reducing ischaemia-reperfusion insult, in humans. Previous research has predominantly used in vitro or animal based models. Aim: This pilot study examines whether dipeptidyl peptidase-IV (DPP-IV) inhibition, slowing the breakdown of endogenous incretins, alters vascular function in obese men. Study design: Crossover, randomised double-blind placebo-controlled study. Method: 15 obese men were recruited (age range:28-72years). Following recruitment participants were randomised to Vildagliptin (100mg/day) or placebo for 12 weeks. At end of the treatment vascular assessments were performed (maximum hyperaemia; endothelial (in)dependent microvascular function; microvascular filtration capacity; capillary density; peak reactive hyperaemia; fovea thickness and applanation tonometry). Following a 4 week washout period the participant received the alternative treatment for 12 weeks. Vascular assessments were repeated within the last 2 weeks of treatment. Results: 14 participants completed the study. Active treatment resulted in a small but significant reduction in HbA1c (Active mean±standard deviation: 38.1±4.8 vs 39.1±4.1mmol/mol, p=0.003 paired T-test). Capillary density was increased with DPP-IV inhibition (n=7, active median(25th,75th centiles) 126 (118,144)mm2 vs placebo 117 (109,142)mm2, p=0.028 Wilcoxon Signed Rank test). There was no significant change in other vascular assessments or fovea thickness Discussion: In this pilot study DPP-IV inhibition successfully reduced HbA1c in obese men. Capillary density significantly increased with Vildagliptin. However, as there were no significant changes in parameters associated with capillary density, namely microvascular filtration capacity, this observation needs to be confirmed with further research.