Clopidogrel in combination with aspirin has been widely used in patients who have undergone coronary stent implantation. However, the benefit to Japanese patients with stable angina (SA) or old myocardial infarction (OMI) undergoing percutaneous coronary intervention (PCI) still remains unclear.The aim of this multicenter, randomized, double-blind, clinical study was to evaluate the safety of a clopidogrel 300 mg loading dose followed by a 75 mg maintenance dose compared to ticlopidine 100 mg twice daily in patients with SA or OMI undergoing PCI who were on aspirin (81 to 100 mg once daily). The primary endpoint was the composite of safety events comprising clinically significant bleeding, blood disorders, elevated liver function values, and study drug discontinuation up to week 12. The key secondary endpoints were major adverse cardiac events (MACE), major adverse cardiac and cerebrovascular events (MACCE), and bleeding events. A total of 1003 patients were randomly allocated to receive either clopidogrel or ticlopidine and 931 patients underwent PCI. The cumulative incidence of the composite safety endpoint in the clopidogrel group was statistically lower than that of ticlopidine (P < 0.0001, hazard ratio; 0.259; 95%CI; 0.187 to 0.359). There were no statistically significant differences between treatments with respect to MACE at week 12 (P = 0.7899) nor to the bleeding events (P = 0.5292, stratified log-rank test).Clopidogrel was found to have a better benefit/risk profile than ticlopidine in Japanese patients with SA or OMI undergoing PCI.