Water management has emerged as a significant challenge in portable direct methanol fuel cells, DMFCs. Excessive water crossover through the membrane causes water loss in the anode and flooding in the cathode. We report a novel DMFC design based on Nafion 112 and a cathode gas-diffusion layer coated with a microporous layer. This DMFC operated with ambient air yielded a stable power density of 56 mW/cm(2) at 60 degrees C, while the net water transport coefficient was only 0.64 compared to a typical value of 3 for Nafion 117 membranes. In addition, the fuel efficiency was about 74-92%. (C) 2004 The Electrochemical Society.