Background and Objectives: Sarpogrelate HCL (Anplag) is a 5-hydroxytryptamine subtype 2A (5-HT2A) receptor antagonist. A previous study reported that adjunctive anplag of 300 mg to aspirin and ticlopidine reduced the rate of in-stent restenosis compared to control group. We sought to assess effects of 300-mg anplag in addition to aspirin and clopidogrel on platelet inhibition in patients underwent drug-eluting stents insertion. Subjects and Methods: This is a randomized, cross-over designed, prospective study. Thirty eligible patients were enrolled and received dual or triple antiplatelet therapies for 2 weeks and then crossed and administered to opposite therapy for 2 weeks. Platelet function tests by multiple electrode aggregometry and light transmittance aggregometry were performed just before and 2 and 4 weeks after administration. Results: Baseline platelet function was measured at 24짹2 hours after administration of loading doses of 300-mg aspirin and 300-mg clopidogrel. We calculated percentage of platelet inhibition (PPI) as a formula: (POST-BASE)/BASE. Preliminary data showed no significant difference in comparison of percentage of platelet inhibition in both groups (table). Final result will be presented. Conclusions: Preliminary data suggested an adjunctive sarpogrelate HCL of 300 mg to aspirin and clopidogrel did not show an additional benefits on laboratory platelet inhibition compared to conventional dual therapy.