Background: Aspirin and clopidogrel have become standard therapy to prevent stent thrombosis in pts undergoing coronary stenting. However, there is heterogeneity in the responses of individual pts to each of these drugs. Also stent thrombosis remains an important and potentially lethal clinical problem. Cilostazol is a potent antipletelet agent that selectively inhibits posphodiesterase III, a mechanism different from clopidogrel. In recent studies, triple antiplatelet therapy seems to be more effective in preventing stent thrombosis compared with the dual antiplatelet regimen. Objective: First, we evaluated the prevalence of aspirin and clopidogrel resistance in Korean pts undergoing coronary stenting. Second, we compared the prevalence of those in pts with the dual and triple antiplatelet regimen. Methods: We enrolled 251 pts scheduled for elective coronary stenting. Patients undergoing successful coronary stenting were divided into dual antiplatelet therapy (aspirin + clopidogrel, group I, n = 86) and triple antiplatelet therapy (aspirin + clopidogrel + cilostazol, group II, n=165) groups. We used the Ultegra Rapid Platelet Function Assay (RPFA)-ASA and the Ultegra RPFA- P2Y12 (VerifyNowTM Assay, Accumetrics Inc. San Diego, California) approved by FDA, to determine aspirin and clopidogrel resistance. The blood sampling was performed 2 weeks after coronary stenting. Aspirin resistance is defined as an ARU (aspirin reaction units) ��� 550. Clopidogrel resistance is defined as the % inhibition is less than 20%. Results: Twenty-five (9.9%) patients were resistant to aspirin, 24 (9.8%) to clopidogrel, and 3 (1.1%) were resistant to both drugs. Eight (9.3%) patients were resistant to aspirin and 13 (16%) to clopidogrel in group I. Seventeen (10.3%) were resistant to aspirin and 11 (7.0%) to clopidogrel in group II. The ARU was not different between groups (436짹71 vs. 440짹66, p=0.591), but the % inhibition was higher in group II (53.3짹29.4 vs. 44.5짹25.2 %, p=0.022). Conclusion: The prevalence of aspirin resistance in pts undergoing coronary stenting was approximately 10%. The prevalence of clopidogel resistance assessed with RPFA-P2Y12 can be reduced with triple antipletelet treatment.