In-stent restenosis is a complication which impairs the success of coronary stenting. Recently, it was supposed that a delayed hypersensitivity reaction to nickel and molybdenum might be one of the triggering factors in in-stent restenosis. We have analyzed the data collected in our centre with respect to this hypothesis. Altogether, 34 patients were investigated (24 male, 10 female). Patch tests were performed with the standard series of the German Contact Dermatitis Research Group and a metal series containing the metal components of 316 L stainless steel. A positive patch test reaction to nickel was observed in 4 (11.8%) patients. None of the patients showed sensitization to the other metals. Retrospective analysis was performed in 20 patients: 2 of these patients had a positive patch test reaction to nickel, one of whom had an in-stent restenosis, and the other not. Restenoses were predominantly observed in patients with negative patch test reactions to nickel (6/18 patients). Out of the patients who were investigated prospectively only one showed sensitization to nickel. Restenosis was observed in 2 patients: neither patient had nickel allergy. Although it still cannot be excluded that metal allergy may play a role in the restenosis process in coronary stenting, there is at present little evidence for it.