The crossover of methanol from anode to cathode is one of the important factors that affects the performance of direct methanol fuel cells that are being developed for portable power and transportation applications. We report an effective method for the determination of methanol permeability through simple electrochemical methods. The method has been applied to find the permeability factors for various methanol concentrations. An optimum concentration of methanol for operation of fuel cells using methanol as the fuel has also been determined based on the above results. (C) 2003 Elsevier Science B.V. All rights reserved.