The methanol diffusion coefficient was measured for Nation and two differently cross-linked polyaryl-blend-membranes developed at ICVT. It could be shown that the methanol diffusion coefficient depends on both temperature and membrane water content. For the polyaryl-blend-membranes the methanol diffusion coefficient is approx. 2-2.5 times lower than for Nation at the same temperature and the same water content. The activation enthalpy for methanol diffusion in Nafion is about 20 kJ mol(-1) and decreases with increasing water content. (C) 2004 Elsevier B.V. All rights reserved.