A five-cell 150 W air-feed direct methanol fuel cell (DMFC) stack was demonstrated. The DMFC cells employed Nafion 117(R) as a solid polymer electrolyte membrane and high surface area carbon supported Pt-Ru and Pt catalysts for methanol electrooxidation and oxygen reduction, respectively. Stainless steel-based stack housing and bipolar plates were utilized. Electrodes with a 225 cm(2) geometrical area were manufactured by a doctor-blade technique. An average power density of about 140 mW cm(-2) was obtained at 110 degreesC in the presence of 1 M methanol and 3 atm air feed. A small area graphite single cell (5 cm(2)) based on the same membrane electrode assembly (MEA) gave a power density of 180 mW cm(-2) under similar operating conditions. This difference is ascribed to the larger internal resistance of the stack and to non-homogeneous reactant distribution. A small loss of performance was observed at high current densities after one month of discontinuous stack operation.