Biocatalyzed electrolysis is a novel biological hydrogen production process with the potential to efficiently convert a wide range of dissolved organic materials in wastewaters. Even substrates formerly regarded to be unsuitable for hydrogen production due to the endothermic nature of the involved conversion reactions can be converted with this technology. Biocatalyzed electrolysis achieves this by utilizing electrochemically active micro-organisms that are capable of generating electrical current from the oxidation of organic matter. When this biological anode is coupled to a proton reducing cathode by means of a power supply, hydrogen is generated. In the biocatalyzed electrolysis experiments presented in this article acetate is used as a model compound. In theory, biocatalyzed electrolysis of acetate requires applied voltages that can be as low as 0.14V, while hydrogen production by means of conventional water electrolysis, in practice, requires applied voltages well above 1.6 V. At an applied voltage of 0.5 V the biocatalyzed electrolysis setup used in this study, produces approximately 0.02 m(3) H-2/m(3) reactor liquid volume/day from acetate at an overall efficiency of 53 +/- 3.5%. This performance was mainly limited by the current design of the system, diffusional loss of hydrogen from the cathode to the anode chamber and high overpotentials associated with the cathode reaction. In this article we show that optimization of the process will allow future volumetric hydrogen production rates above 10m(3)H(2)/m(3) reactor liquid volume/day at overall efficiencies exceeding 90% and applied voltages as low as 0.3-0.4V. In the future, this will make biocatalyzed electrolysis an attractive technology for hydrogen production from a wide variety of wastewaters. (c) 2006 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.