Various pretreatment methods have been investigated for their effects on the performances of direct methanol fuel cells (DMFCs) under passive and air-breathing conditions. Performance of the passive cell was very much influenced by the pretreatment conditions which included exposure of the membrane-electrode assembly either to water or to a methanol solution prior to use. By carrying out the pretreatment processes the cells were activated to attain their maximum performances in a very short time. However, the time to reach maximum performance and the maximum value obtained were dependent on the pretreatment conditions. The pretreatment process is considered to give rise to changes both in the electrode structure and the degree of hydration of the polymer electrolyte, leading to activation of the MEA. (C) 2004 Elsevier Ltd. All rights reserved.