The previously developed mathematical model, based on our physical model, is validated by comparing simulations to experiments. The mathematical model is placed within a simple pseudo-two-dimensional fuel-cell (FC) model. The comparisons mainly involve the net flux of water per proton in the membrane. In the complete FC model, there is only one fitting parameter, the transport coefficient (effective permeability) of the diffusion media, and it is fit at only one simulation condition for each FC setup. The simulations agree very well with both values and trends taken from various literature sources under many different operating conditions, including pressure, temperature, current density, and inlet humidification and stoichiometry. Furthermore, the model allows for an explanation of those trends. The sensitivity and the details of the mathematical model are also examined. Overall, the mathematical model and the physical model are validated and shown to be generally applicable for describing water transport in a polymer-electrolyte membrane. (C) 2004 The Electrochemical Society.