Platinum-based membrane-electrode assemblies have been prepared to make electrochemical measurements of breath alcohol levels. Measurements are made by using a solid polymer electrolyte ethanol-air fuel cell. A diffusion membrane is placed in the feed compartment to limit the cell response by ethanol diffusion. The cell is found suitable for the realization of gaseous ethanol sensors. Reproducible cell responses are obtained over several hundreds of cycles. The cell current is proportional to the ethanol concentration in the feed compartment and to the thickness of the diffusion membrane. The transient response of the cell is simulated using Fickian phenomenological equations. Calculated results are in good agreement with experimental data.