Background: Some evidences suggested that low response to clopidogrel assessed by VerifyNow P2Y12 assay (Accumetrics Inc, CA) is associated with recurrent atherothrombotic events after drug eluting stent implantations. It is obscure whether VerifyNow P2Y12 assay is sufficiently reproducible over time to be a useful predictive test in case of low response to clopidogrel. Methods: We enrolled 59 patients (41 males, 62.5짹10.7 years) with low response to clopidogrel and DES implantations. Low response to clopidogrel was defined as the less than 20% inhibition of P2Y12 receptor or more than 235 IU of post-treatment P2Y12reaction unit (PRU) assessed by VerifyNow P2Y12 assay. We re-tested the same patients using identical methods and after 1-24 month (mean: 238 days) to determine whether the results of the individual tests are consistent over time. Agreement between the tests was determined by kappa value and Spearman rank correlation. All patients prescribed the same medication included standard dual anti-platelet therapy (aspirin 100mg and clopidogrel 75mg) at baseline and re-tested. Results: Post-PRU value shows moderate agreement (kappa value: 0.42, p<0.01) and statistically significant correlation (r=0.49, p <0.01) at baseline and retest. However, percent inhibition of P2Y12 receptor shows fair agreement (kappa value: 0.26, p<0.01) and no significant correlation (r=0.25, p>0.05) at the same period. Conclusion: Post-PRU value is moderate reproducible over time to be a useful predictive test in patients with low response to clopidogrel assessed by VerifyNow P2Y12 assay and DES implantation.