The cogeneration of hydrogen and methane from protein-mixed food waste by two-phase anaerobic fermentation was investigated for the first time in this paper. The hydrogen-producing bacteria derived from activated sludge were used to produce hydrogen from defatted milk powder (DMP) in the first stage, and Saccharomyces cerevisiae was used to promote the hydrogen production. The hydrogen yield from DMP with S. cerevisiae is promoted from 171.9 ml/g-TVS to 186.1 ml/g-TVS, while the peak hydrogen rate is promoted from 47.9 ml/h to 81.3 ml/h. The residual solutions from the first H(2)-producing stage were reutilized by methanogen community to further produce methane in the second stage. Over 96 wt % of acetic acid and butyric acid in the residual solution from DMP with S. cerevisiae are reutilized to give a methane yield of 209.7 ml/g-TVS and peak methane rate of 411.7 ml/d. The cogeneration of hydrogen and methane from DMP markedly increases the energy conversion efficiency from 10.85-11.75% in only hydrogen production to 55.58-61.96%. Because lactose in DMP cogenerates hydrogen yield of 236.5 ml/g-TVS and methane yield of 263.7 ml/g-TVS, it is concluded that lactoprotein in DMP cogenerates hydrogen yield of 136.5 ml/g-TVS and methane yield of 157.8 ml/g-TVS by two-phase fermentation. (C) 2009 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.