The water management in an operating polymer electrolyte fuel cell was studied by small-angle neutron scattering (SANS). The experiments were conducted at 80 degrees C under pressure (1.5 bar) using non-humidified gases and porous gas distributors. The parameters under study were the gas distributor porosity, the membrane thickness, the nature of the electrodes and the gas flow. SANS is shown to be a powerful technique to determine in situ the amount of water in the cell, to differentiate the water located within and outside of the membrane and its distribution across the membrane thickness. The data analysis leads to the determination of water concentration profiles across the membrane that could be used to validate mass transfer models. It is shown that a significant current can be extracted with a dry membrane, porous gas distributors and dry gases and that the membrane does not significantly swell whatever the electric load. (c) 2008 Elsevier B.V. All rights reserved.