Background and Aim: : Celecoxib does not inhibit thromboxane(TX) A2 production in platelets, while it suppresses prostacyclin production in endothelial cells. Therefore, concerns have been raised about the cardiovascular risk of celecoxib. However, celecoxib���s effect on platelet aggregation and prostanoids production and its interaction with other antiplatelet agents are not fully evaluated yet. Methods and Results: Twenty-four volunteers (mean age: 25 years, male: 42%) were allocated into celecoxib (C: n=8), celecoxib+aspirin (A: n=8) and celecoxib+aspirin+clopidogrel (P: n=8). Celecoxib, aspirin and clopidogrel were given 400mg twice a day, 100mg a day and 75mg a day, respectively for 7 days. Platelet aggregation response to adenosine 5'-diphosphate and collagen, and urinary levels of 11-dehydro thromboxane(TX) B2 and 6- keto prostaglandin (PG) F1慣 were measured at baseline and after 7days of medication. There were no significant changes in platelet aggregation (94.5짹22.7% vs 74.6짹18.5%; p=0.233), and urinary prostanoids excretion in C group. In A and P groups, there were significant inhibition of platelet aggregation (A: 82.0짹7.9% vs 51.1짹12.1%, p<0.05; P: 85.8짹22.1% vs 26.8짹8.7%; p<0.05) and prostanoids production (see table). Conclusion: Celecoxib does not alter platelet aggregation and prostanoids production and does not interfere with the antiplatelet effect of aspirin or clopidogrel. So, concomitant use of celecoxib seems to be safe with aspirin or clopidogrel.