Background: Point-of-care analyses might be helpful to guide tailored individual antiplatelet treatment in patients undergoing percutaneous intervention (PCI) with drug-eluting stents due to interindividual variation of platelet responsiveness to thienopyridines. Methods and Results: We collected 36 healthy volunteers and 113 consecutive patients undergoing PCI from Dec. 2008 to Jul. 2009. Platelet function tests were performed according to serial time points, various loading and maintenance doses by light transmission aggregometry (Chrono-Log, Havertown, PA, USA), VerifyNow짰 system assay (Accumetrics, San Diego, CA, USA) and Multiple electrode aggregometry (Dynabyte, Munich, Germany). In PCI patients, adjunctive loading dose of 200 mg-cilostazol to aspirin and clopidogrel versus traditional treatment improved platelet responsiveness to antiplatelet agents (table). Additional loading of 200 mg cilostazol to 300 mg clopidogrel had a similiar inhibitory effect with clopidogrel 600 mg loading dose after 6 hours (figure). Parameters among three devices of platelet function testing had strong correlations. Conclusion: Laboratory responsiveness to antiplatelet agents depended upon loading doses and timing. Therefore, the monitoring of platelet reactivity by point-of-care analysis might be important in clinical practice.