A single liquid chamber microbial fuel cell (MFC) with a gas-collection compartment was continuously operated under electrically assisted conditions for hydrogen production. Graphite felt was used for anode construction, while the cathode was made of Pd/Pt coated Toray carbon fiber paper with a catalyst loading of 0.5 mg cm(-2). To achieve hydrogen production, the MFC was connected to a power supply and operated at voltages in a range of 0.5-1.3 V. Either acetate or glucose was used as a source of carbon. At an acetate load of 1.67 g(L(A)d)(-1), the volumetric rate of hydrogen production reached 0.98 L-STP (L(A)d)(-1) when a voltage of 1.16 V was applied. This corresponded to a hydrogen yield of 2 mol (mol-acetate)(-1) with a 50% conversion efficiency. Throughout the experiment, MFC efficiency was adversely affected by the metabolic activity of methanogenic microorganisms, which competed with exoelectrogenic microorganisms for the carbon source and consumed part of the hydrogen produced at the cathode. Crown Copyright (C) 2008 Published by Elsevier B.V. All rights reserved.