Although many patients with coronary artery disease are being treated by coronary stents, in-stent restenosis is the major limitation of percutaneous coronary stenting procedures. Most stents are made of stainless steel, and that, allergic reactions to nickel ions released from coronary stainless-steel stents may be one of the triggering mechanisms for in-stent restenosis. We aimed to evaluate the relationship between in-stent restenosis and nickel allergy in a prospective study. For this purpose, we applied epicutaneous patch test for nickel in 43 patients who had undergone elective intracoronary stent placement for stable angina pectoris in the day following stent placement and evaluated the presence of nickel allergy. Control angiography was performed at 6 months to determine in-stent restenosis. Three (6.9%) patients had allergic reaction to nickel and 16 (37%) patients had developed in-stent restenosis. One of the 3 patients with nickel allergy had diffuse in-stent restenosis and the others not. The present study therefore does not support the proposed relationship between nickel allergy and development of in-stent restenosis in patients having stainless steel stents. Large scale studies are needed to reach a final conclusion.