Electrochemical studies on low catalyst loading gas diffusion electrodes for polymer electrolyte fuel cells are reported. The best performance is obtained with an electrode formed from 20 wt % Pt/C, 0.4 mg Pt cm(-2) and 1.1 mg Nafion(R) cm(-2) in the catalyst layer and 15% PTFE in a diffusion layer of 50 mu m thickness, for both the cathode and the anode. However, it is also observed that the platinum requirement can be diminished to values close to 0.2 mg Pt cm(-2) in the cathode and 0.1 mg Pt cm(-2) in the anode, without appreciably affecting the good characteristics of the fuel cell response. The experimental fuel cell data were analysed using theoretical models of the electrode structure and of the fuel cell system. It is seen that most of the electrode systems present limiting currents and some also show linear diffusion components arising from diffusion limitations in the gas channels and/or in the thin him of electrolyte covering the catalyst particles.