Studies on hydrogen production in an anaerobic sequencing batch reactor (AnSBR) indicated that the anaerobic acidogenic conversion of sucrose could produce hydrogen. The hydrogen production of acclimated sewage sludge depended on hydraulic retention time (HRT) and reaction period/settling period (R/S) ratio. A short equivalent HRT, even up to 4 h, gave good hydrogen productivity and high hydrogen production rate (HPR) values. For each equivalent HRT, R/S ratio control also increased the hydrogen productivity and HPR. Reactor operation at an intimate control of HRT and R/S ratio was preferable for hydrogen production. At HRT S h, R/S ratio 5.6 and an organic loading rate of 0.23 mol-sucrose dm(-3) day(-1), each mole of sucrose in the mesophilic hydrogenic reactor yielded 2.6 mole of hydrogen; each gram of biomass produced 0.069 mole of hydrogen per day. (C) 2003 Society of Chemical Industry.