 Dual antiplatelet therapy with aspirin and thienopyridines decreases the rate of stent thrombosis in patients undergoing percutaneous coronary intervention PCI. However, despite intensified antiplatelet treatment, some of the patients undergoing PCI develop thrombotic stent occlusion, suggesting incomplete platelet inhibition due to thienopyridine resistance. The present study is designed in order to clarify the influence of CYP2C19 genetic polymorphism on the several biomarkers for platelet activation in Japanese patients treated with thienopyridines undergoing elective PCI. 