We report a micro-Raman spectroscopic study of a fuel cell membrane subjected to fuel cell testing until a significant decline in efficiency was noted. The membrane, poly(vinylidene fluoride)-graft-poly(styrene sulfonic acid), PVDF-g-PSSA, was produced by electron irradiation of a PVDF film, grafting with polystyrene and subsequent sulfonation. Depth profiles show that severe degradation due to loss of polystyrene sulfonic acid has occurred during the fuel cell run. The remaining amount of polystyrene sulfonic acid is of the order of 5-10% of the initial content. Confocal Raman spectroscopy is found to be an excellent tool for investigating the changes in membrane composition after fuel cell experiments. (C) 2000 Elsevier Science Ltd. All rights reserved.