A simple electrochemical method for the measurement of the permeability of methanol in proton exchange membranes equilibrated with a supporting liquid electrolyte at elevated temperatures is proposed. Carbon supported platinum working electrodes are placed to both sides of the membrane sample and serve as concentration sensors. Methanol is added to one or both sides of the membrane and the permeability is calculated from the time responses of anodic peak currents on the two working electrodes. Experimental results are given for Nafion(R) 117 perfluorosulfonate membrane in 2.0 M H2SO4 at 60 and 70 degrees C.