A new method to analyze deteriorated direct methanol fuel cells (DMFCs) by combining electrochemical impedance analysis and physicochemical investigations is proposed. To make a comparison, one pristine membrane electrode assembly (MEA) and one deteriorated MEA, following 1000 h of continuous operation, were prepared. A unique impedance analysis enabled the separation of the impedance values for the cathode and the anode, and it was possible to determine that the deterioration of the MEA mainly came from the deterioration of the cathode. Several physicochemical investigations were made to show the relationship between the electrochemical properties and the deterioration of the MEA. (c) 2006 Elsevier B.V. All rights reserved.