In order to observe the performance of the anode and cathode during actual direct methanol fuel cell (DMFC) operating conditions and to minimize the polarization of the reference electrode, we used a reversible hydrogen reference electrode (RHE) with its instability minimized. For analysis of the I-V polarization curve of each electrode, Tafel plots were used as the diagnostic tool. According to the slopes in the Tafel plot, the I-V polarization curves of each electrode were divided into the several regions. The effects of operating parameters on the performance of each electrode were interpreted in terms of mass transfer and electrode activation. The methanol and oxygen crossover through the membrane significantly affected the performance of the cell. (c) 2005 Elsevier B.V. All rights reserved.