Background : Effective antiplatelet regimen is an emeging issue in the drug-eluting stent (DES) era. Stent thrombosis was increased in chronic renal failure (CRF) which may be attributed to poor response to clopidogrel. The mechanisms leading to poor clopidogrel effects are not fully elucidated and are likely multifactorial. Objectives : We sougt to compare clopidogrel responsiveness between chronic renal failure patients and normal renal function subjects using VerifyNowTM P2Y12 assay. Methods : We conducted a prospective, randomized, open-label, single center trial to evaluate the difference of clopidogrel responsiveness according to clopidogrel dose in CRF patients. 23 normal renal function patients with standard dose clopidogrel, 75mg daily (group 1, 61짹7 years ) and 36 CRF subjects (60짹5 years) divided into two groups according to clopidogrel dose (Group 2: 18 subjects with 75mg, Group 3: 18 subjects with 150mg daily for 30days) were enrolled. And, we evlauated the clopidogrel reponsiveness according to clopidogrel 300mg loading in CRF patients(control 10, and CRF 10 patients). The primary efficacy variable was mean PRU (P2Y12 Reaction unit) and % inhibition difference between each groups using VerifyNowTM P2Y12 Assay. Results : There was significant PRU difference between each three groups ( 239짹87 in group 1, 308짹70 in group 2, 302짹81 PRU in group 3, p= 0.013) and significant difference of % inhibition ( 35짹20 in group 1, 21짹16 in group 2, 23짹14 % in group 3, p= 0.026). There was good positive correlation between serum creatinine and PRU (r=0.435, p=0.001) and fair negative correlation between serum creatinine and % platelet inhibition (r=-0.363, p=0.005). Results of clopidogrel responsiveness of loading dose will be presented. Conclusions : Clopidogrel responsiveness was more decreased in CRF patients than non-CRF patients. The PRU and % platelet inhibition were correlated with serum creatinine level.