A sufficient life time of the membrane-electrode assemblies (MEA) for polymer electrolyte fuel cells (PEFC) is necessary for using PEFC in mobile or stationary power supplies. During the life time, the electrochemical performance should be stable and the operation behavior should not change. But in real operation, the electrochemical performance decreases and the operation behavior changes. These effects are induced by a degradation of fuel cell components, which makes necessary to study the structural and chemical changes of single components affected by electrochemical stressing for understanding the degradation mechanisms and effects. The catalyst in the electrodes is the essential component dominating the fuel cell reaction. In both electrodes, platinum is used as catalyst, therefore changes of the catalyst or catalyst distribution must be investigated. The MEAs were operated in single cells in full automatic test facilities. After fuel cell operation. electrodes and MEAs were characterized physically by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX) and chemisorption measurements. An alteration of the platinum distribution and a migration of the platinum was observed after fuel cell operation. (C) 2003 Elsevier B.V. All rights reserved.