The effect of Nafion loading in the catalyst layer of cathodes for polymer electrolyte fuel cells (PEFCs) was investigated. Steady-state galvanostatic polarisation (GP), electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) measurements were carried out at 25 degrees C in 1.0 M H2SO4 on electrodes with different Nafion loadings. EIS supplied information on the polarization resistance and CV on the electrochemical active area for the oxygen reduction reaction (ORR). These parameters, together with those derived from GP, allowed a better identification of the features governing the ORR. An optimum Nafion loading was identified. This loading was found to correspond to a minimum in the polarization resistance and in the oxygen reduction overpotential and ct maximum in the electrochemical active area.