Backgroud: We investigated whether endothelial dysfunction was related to the DES at 6 months after stenting. Methods: In 75 (male 31, 62.1짹9.5 yrs) patients treated with DESs to the LAD (39 SES, 36 PES) and 134 control patients without stenting (male 61, 61.2짹11.2 yrs), endothelial function was estimated at 6 months after stenting, by incremental Ach infusion (A1: 20, A2: 50, A3: 100 µg/min) and nitrate (200 µg/min) into the left coronary ostium. The infusion was stopped if > 90 % vasoconstriction was induced. The vascular response was measured in the arterial segment 2 mm proximal and distal to the DESs and compared with the matched segments of controls. All antianginal agents were withheld for 72 hours prior to CAGs. Results: There was a greater vasoconstriction to Ach in both SES and PES groups than controls (p<0.001, Figure). The vasoconstriction to Ach was more prominent in the arterial segment distal than proximal to the DESs in both SES and PES groups (p<0.001, Figure). There were no differences of vasoconstriction to Ach between SES and PES groups (Figure). Endothelium-independent vasodilatation to nitrates did not differ significantly between DES group and controls (p=0.211). There were no differences of risk factors between two groups. Conclusions: There was an abnormal vasoconstriction to Ach in both SES and PES, especially in the arterial segment distal to the DESs at 6 months after stenting, suggesting a potential long term adverse effects of DES on local coronary endothelial dysfunction.