Background Nuclear factor-κB (NF-κB) plays a pivotal role in restenosis after percutaneous coronary intervention (PCI) and the aim of the present clinical trials was to evaluate the effectiveness of a NF-κB decoy for preventing restenosis. Methods and Results The initial case was a patient suffering from effort angina who had stenoses in the proximal and middle portions of the right coronary artery. The patient received 2 stents; the NF-κB decoy was delivered to the distal site, but not the proximal site. Six months after the PCI, the NF-κB decoy had suppressed restenosis in comparison with the no-decoy transfection site. The second case was a patient who underwent single-stent insertion and decoy transfection at the same site, and minimal intimal thickening was observed at 6 month after PCI. No systemic adverse effects were observed in either case. Conclusion These results indicate the clinical usefulness and safety of NF-κB decoy transfection after PCI, but further evaluations are necessary to confirm its clinical effectiveness. (Circ J 2004; 68: 270 - 271)