Water-content profiles across the membrane electrode assembly of a polymer-electrolytefuel cell were measured using high-resolution neutron imaging and compared to mathematical-modeling predictions. It was found that the membrane held considerably more water than the other membrane-electrode constituents (catalyst layers, microporous layers, and macroporous gas-diffusion layers) at low temperatures, 40 and 60 degrees C. The water content in the membrane and the assembly decreased drastically at 80 degrees C where vapor transport and a heat-pipe effect began to dominate the water removal from the membrane-electrode assembly. In the regimes where vapor transport was significant, the through-plane water-content profile skewed towards the cathode. Similar trends were observed as the relative humidity of the inlet gases was lowered. This combined experimental and modeling approach has been beneficial in rationalizing the results of each and has given insight into future directions for new experimental work and refinements to currently available models. (C) 2008 Elsevier Ltd. All rights reserved.