The present work reports a systematic experimental analysis on water transport in a phosphoric acid doped polybenzimidazole-based high temperature PEM fuel cell. Two sets of polarization curves are run with dry and alternatively humidified reactants, covering a wide range of fuel cell operating temperatures and stoichiometries. With dry feed streams, up to 18% of water produced by electrochemical reaction is found on anode side proving the presence of water transport from cathode electrode. Under the investigated conditions, water transport across the membrane is independent of fuel cell temperature but strongly dependent on reactants stoichiometry and humidification. Such parameters can even determine a change in water transport direction. Humidification causes a limited drop in membrane proton resistivity (around 6 m Omega cm(2)); conversely a slight decrease in fuel cell performances (-5 to 20 mV) is measured. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.