The model of reactants' diffusion through porous gas diffusion and catalytic layers of the fuel cell with proton exchange membrane is developed. Transfer processes in these layers are considered with the use of percolation theory. In particular, it was shown that three systems of interconnected particles or volumes catalyst, electrolyte and pores, should be created in the catalyst layer. The process of flooding of the porous system by water produced during the fuel cell operation is examined. The developed model enables to predict the influence of structural parameters of the layer on fuel cell performance. (c) 2005 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.