Hydrogen and methane co-production from potato waste was examined using a two-stage process of anaerobic digestion. The hydrogen stage was operated in continuous flow under a pH of 5.5 and a HRT of 6 h. The methane stage was operated in both continuous and semi-continuous flows under HRTs of 30 h and 90 h, respectively, with pH controlled at 7. A maximum gas production rate of 270 ml/h and an average of 119 ml/h were obtained from the hydrogen stage during the operation over 110 days. The hydrogen concentration contained in the gas was 45% (v/v), on average. The maximum and average gas production rates observed from methane reactor during the 74 days of semi-continuous flow operation were 187 and 141 ml/h, respectively, with an average methane concentration of 76%. Overall, 70% of VS, 64% of total COD in the feedstock were removed. The hydrogen and methane yields from the potato waste were 30 l/kg TS (with a maximum of 68 l/kg) and 183 l/kg TS (with a maximum of 225 l/kg), respectively. The total energy yield obtained was 2.14 kW h/kg TS, with a maximum of 2.74 kW h/kg TS. (C) 2007 Elsevier Ltd. All rights reserved.