The water balance of a polymer electrolyte fuel cell operated on pure H-2/O-2 has been investigated in coflow and counterflow mode for different gas humidifications by using locally resolved impedance spectroscopy. The locally resolved impedance spectra show that the strongly decreasing performance with decreasing humidification in coflow mode can be mainly attributed to drying of the membrane and the catalyst layers in the gas inlet region. In contrast, the internal humidification in counterflow mode provides a rapid decrease in ohmic and charge-transfer resistance at the gas inlets and by this allows higher performance, even at low gas humidity. (c) 2005 The Electrochemical Society.