The aim of this study was to determine the possibility of applying psychrophilic bacteria for hydrogen production in whey biofermentation process. Experiments were conducted in 500-mL anaerobic respirometers at a temperature of 20 degrees C. The initial organic load of fermentation tanks reached 10 g COD/L. Depending on the experimental variant, analyses were carried out for psychrophilic bacteria isolated from underground water and from demersal lake water that represented Gammaproteobacteria class - Rahnella aquatilis (9 strains) and Firmicutes phylum: Carnobacterium maltaromaticum, Trichococcus collinsii and Clostridium algidixylanolyticum. The effectiveness of biogas production was diversified and strain-specific, ranging from 126.48 to 4737.72 mL/g bacterial biomass. The highest concentration of H-2 in biogas, ranging from 65.15% to 69.12% and effectiveness of H-2 production from 1587.47 to 3087.57 mL/g bacterial biomass, were determined for R. aquatilis strains isolated from the demersal lake water. The lowest H-2 concentration in the gaseous metabolites, i.e. 15.46% to 20.70%, was noted for bacteria of the phylum Firmicutes. Copyright (C) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.