State of the art MEAs were aged in a fuel cell vehicle and degradation effects analyzed using electron microscopy and electrochemical methods. All cells of the stack showed a performance decay along with a loss in the electrochemical surface area. This could be correlated to particle growth and carbon corrosion observed by electron microscopy. Spatially resolved investigations showed a significant deterioration of the cathode, which is particularly pronounced at the hydrogen inlet. Differences in the cell performance of the aged cells could not be attributed to a variation in the catalyst degradation, but are linked to an altered ohmic resistance in the cells. The ohmic resistance of the cells is likely to be affected by the formation of precipitates in the membrane and seems to be correlated with their size. (C) 2009 Elsevier B.V. All rights reserved.