This paper presents a study of the effects of an organic contaminant containing an amide bond (-CONH-), epsilon-caprolactam, on polymer electrolyte membrane fuel cells (PEMFCs). The epsilon-caprolactam has been detected in leachates from polyphthalamide materials that are being considered for use as balance-of-plant structural materials for PEMFCs. Contamination effects from epsilon-caprolactam in Nafion membranes are shown to be controlled by temperature. A possible explanation of the temperature effect is the endothermic ring-opening reaction of the amide bond (-NHCO-) of the cyclic epsilon-caprolactam. UV-vis and ATR-IR spectroscopy studies confirmed the presence of open ring structure of epsilon-caprolactam in membranes. The ECSA and kinetic current for the ORR of the Pt/C catalyst were also investigated and were observed to decrease upon contamination by the epsilon-caprolactam. By comparison of the CVs of ammonia and acetic acid, we confirmed the adsorption of carboxylic acid (-COOH) or carboxylate anion (-COO-) onto the surface of the Pt. Finally, a comparison of in situ voltage losses at 80 degrees C and 50 degrees C also revealed temperature effects, especially in the membrane, as a result of the dramatic increase in the HFR. (C) The Author(s) 2015. Published by ECS. All rights reserved.