The characteristics of water balance in the solid polymer electrolyte and its effects on the performance of a polymer electrolyte fuel cell are investigated by means of electrochemical impedance spectroscopy (EIS) and current pulse method (CPM). At high current densities, the water content on the anode side of the electrolyte decreases due to electroosmotic drag and the limited backtransport properties of the polymer. This results in a higher membrane resistance as well as in an increased anode overpotential due to a loss in active surface. We also describe some first means to overcome these problems. (C) 2003 Elsevier B.V. All rights reserved.