Investigations are presented to determine the dependence of the performance of direct methanol fuel cells (DMFCs) and the methanol cross-over rate on the operating conditions, on the structure of the electrodes and on the noble-metal loading. It is shown that performance and methanol permeation depend strongly on cell temperature and cathode air flow. Also, methanol permeation can be reduced significantly by varying the anode structure, but the changed electrode structure also leads to somewhat lower power densities. The metal loading is varied at the anode and cathode affecting the cell performance. Furthermore, the differences between supported and unsupported catalysts are compared. We discuss the optimum conditions for the DMFC operation considering the various important factors. The discussion is focussed on finding a compromise between fuel cell performance, fuel utilization and metal loading. (C) 2003 Elsevier B.V. All rights reserved.