We studied the relation between renin-angiotensin system (RAS) related gene polymorphisms, such as angiotensin converting enzyme (ACE) insertion/deletion (I/D), angiotensinogen (AGT) M253T and angiotensin II type 1 receptor (AT1R) A1166C, and the effect of quinapril, an ACE inhibitor with high tissue-binding affinity, on preventing restenosis after percutaneous coronary intervention (PCI). A total of 253 patients successfully treated for coronary artery disease were randomly assigned to quinapril or control. Of the 215 patients who completed the follow-up, we determined gene polymorphisms in 204 patients with 241 lesions who provided blood samples for genotype determination. In the control, the ACE D homozygotes showed a smaller minimal lumen diameter (MLD) at follow-up (P=0.063). The other two genotypes of AGT and AT1R did not affect restenosis after PCI. According to quinapril treatment, the AGT T homozygotes significantly showed a beneficial effect of quinapril on MLD (P=0.013) and late lumen loss (P=0.013). The ACE I homozygotes also exhibited beneficial effects of quinapril on larger MLD (P=0.065). The AT1R genotype did not influence the quinapril effect. In conclusion, the AGT T homozygotes might benefit from effects of quinapril on preventing restenosis after PCI.