Endothelial progenitor cell (EPC) dysfunction is an important mediator of vascular disease in diabetes. We aimed to elucidate the mechanism of adhesion of EPC to diabetic and non-diabetic arteries and to study the effect of the anti-diabetic drug pioglitazone. Peripheral blood mononuclear cells were isolated from healthy donors. Human internal mammary arteries (HIMA) were isolated from patients who underwent coronary artery bypass surgery. EPC were labelled with 111In-oxine and perfused to HIMA in a perfusion chamber. Stromal derived factor-1 (SDF-1) and cyclooxygenase-2 (COX-2) were assessed by immunohistochemical analysis. CXCR-4 expression was assessed by flow cytometry. Adhesion of EPC was increased in HIMA from diabetic patients and was reduced after preincubation with 15 mM glucose for 72 h. EPC adhesion and CXCR-4 expression were inversely correlated. COX-2 and SDF-1 immunostaining in HIMA were positively correlated. Pioglitazone (1 microM) increased the adhesion of EPC to HIMA and the expression of CXCR-4 in EPC. Therefore, EPC-recruiting capability is increased in diabetic arteries, although EPC adhesion is notably impaired by high glucose concentrations. Interestingly, pioglitazone treatment enhances EPC adhesiveness.