BACKGROUND: Effective antiplatelet regimen is an emerging 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. 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, 67짹9 years ) and 27 CRF subjects (63짹7 years) divided into two groups according to clopidogrel dose (Group 2: 13 subjects with 75mg, Group 3: 14 subjects with 150mg daily) were enrolled. All patients was administered clopidogrel for 30 days. The primary efficacy variable was mean PRU (P2Y12 Reaction unit) and % inhibition difference between each groups using VerifyNowTM P2Y12 Assay. RESULTS: There was no significant PRU difference between each three groups ( 239짹87 PRU in group 1, 307짹86PRU in group 2, 302짹95 PRU in group 3, p= 0.056). But, comparing normal subject group with CRF group, significantly increased in CRF group (239짹87 in control, 304짹89 PRU in CRF, p=0.016). There was good positive correlation between serum creatinine and PRU (r=0.438, p=0.003) and fair negative correlation between serum creatinine and % platelet inhibition (r=-0.334, p=0.025). And, the duration of dialysis and PRU were correlated positively (Spearman's rho=0.320, p=0.03). CONCLUSION: The plavix resistance was more increased in CRF patients than non-CRF patients. The PRU and % platelet inhibition were correlated with serum creatinine level and the duration of dialysis.