Hydrogen production from food waste by the mesophilic and thermophilic acidogenic culture acclimated with food waste at 5 days HRT for the effect of pH and volatile solid (VS) concentrations was evaluated. The biogas produced from the thermophilic acidogenic culture was free of methane at all tested pH and VS concentrations, but methane was detected from the mesophilic acidogenic culture at all tested pH. The amount of hydrogen production from the thermophilic acidogenic culture was much higher than that from the mesophilic culture at all tested pH because of the methane free condition and negligible propionate production. Increase of VS concentrations from 3 to 10 g VS l(-1) resulted in the increase of quantity and quality of hydrogen production. The maximum hydrogen content was 69% (v/v) at 10 g VS l(-1). The hydrogen yield was in the range of 0.9-1.8 mol-H-2/mol-hexose and peaked at 6 g VS l(-1). Normal butyrate was the main acid product, and the percentages of butyrate, acetate and propionate at tested VS concentrations were 54-60%, 22-31% and 0.3-1%, respectively. Hydrogen producing microorganisms of Thermoanaerobacterium thermosaccharolytium and Desu fotomaculum geothermicum were detected from the thermophilic acidogenic culture, while Thermotogales strain and Bacillus species were detected from the mesophilic acidogenic culture by PCR-DGGE analysis. (C) 2003 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.