Background: Platelets are actively involved in endothelial dysfunction and vascular atherosclerosis. We aimed to investigate the relationship between high on-treatment platelet reactivity (HOPR) and endothelial function of the peripheral arteries. Methods: Ninety-one patients who planned to take follow-up angiography were consecutively enrolled. All patients were treated with 100mg aspirin and 75mg clopidogrel for at least 6 month due to prior coronary stent implantation. High-sensitivity C-reactive protein (hsCRP) was examined before coronary angiography. HOPR was defined as maximal platelet aggregation by 5 關mol/L of ADP > 50% by light transmittance aggregometry. Flow-mediated dilation (FMD) of the brachial artery was assessed using ultrasonography. Brachial-ankle pulse wave velocity (PWV) was measured using an automated device. Results: There was no difference in baseline characteristics and previous coronary intervention data between ADP-induced platelet aggregation ��� 50 % (group 1, n=59) and HOPR (group 2, n=32). Group 2 showed significantly higher hsCRP levels than group 1. In group 2, significantly lower FMD (6.1 짹 4.1 vs 12.9 짹 6.2 %) and higher PWV (1925.4 짹 362.2 vs 1571.0 짹 306.5 ms) values were noted compared with group 1 (Figure). Platelet reactivity showed negative correlation with FMD and positive correlation with PWV. In follow-up angiography, repeated coronary intervention was more performed in patients with HOPR. Conclusions: Inflammation, endothelial dysfunction and recurrent ischemic events were significantly associated with HOPR in patients under chronic clopidogrel treatment.