This study demonstrates hydrogen production in a membrane-less continuous flow microbial electrolysis cell (MEC) with a gas-phase cathode. The MEC used a carbon felt anode and a gas diffusion cathode with a Pt loading of 0.5 mg cm(-2). No proton exchange membrane (PEM) was used in the setup. instead, the electrodes were separated by a J-cloth. The absence of a PEM as well as a short distance maintained between the electrodes (0.3 mm) resulted in a low internal resistance of 19 Omega. Due to an improved design, the volumetric hydrogen production rate reached 6.3 L(STP) L(A)(-1) d(-1). In spite of the PEM absence, methane concentration in the gas collection chamber was below 2.1% and the presence of hydrogen in the anodic chamber was never observed. Crown Copyright (c) 2008 Published by Elsevier Ltd on behalf of international Association for Hydrogen Energy. All rights reserved.