In this work, it has been shown that the temperature (ranging from 100 to 175 degrees C) greatly influences the performance of H3PO4-doped polybenzimidazole-based high-temperature polymer electrolyte membrane fuel cells by several and complex processes. The temperature, by itself, increases H3PO4-doped PBI conductivity and enhances the electrodic reactions as it rises. Nevertheless, high temperatures reduce the level of hydration of the membrane, above 130-140 degrees C accelerate the self-dehydration of H3PO4, and they may boost the process of catalyst particle agglomeration that takes place in strongly acidic H3PO4 medium (as checked by multi-cycling sweep voltammetry), reducing the overall electrochemical active surface. The first process seems to have a rapid response to changes in the temperature and controls the cell performance immediately after them. The second process seems to develop slower, and influences the cell performance in the "long-term". The predominant processes, at each moment and temperature, determine the effect of the temperature on the cell performance, as potentiostatic curves display. "Long-term" polarization curves grow up to 150 degrees C and decrease at 175 degrees C. "Short-term" ones continuously increase as the temperature does after "conditioning" the cell at 125 degrees C. On the contrary, when compared the polarization curves at 175 degrees C a continuous decrease is observed with the "conditioning" temperature. A discussion of the observed trends is proposed in this work. (c) 2006 Elsevier Ltd. All rights reserved.