The main objective pursued in this work is to investigate the hydrogen production potential from sewage sludge by applying downdraft gasification technique. An experimental study was conducted using a pilot scale (5 kWe) throated downdraft gasifier. During the experiments, all data were recorded with an analog to digital (ATD) converter linked to a computer for every 15 s. The flow rates of the wet product gas, the mass flow rate and volumetric percentage of hydrogen were determined and illustrated. The effects of temperatures of oxidation zone on the production of hydrogen were discussed, and the conversion ratios of dried sewage sludge to hydrogen and ash were also designated. It was concluded that substantial amount of hydrogen gas could be produced utilizing a renewable biomass source such as dried and undigested sewage sludge pellets by applying air blown downdraft gasification technique. The product gas obtained mainly consists of H-2, N-2, CO, CO2 and CH4 with a maximum average gross calorific value of 4 MJ/m(3). Around 10-11%(V/V) of this product gas is hydrogen which could be utilized for fuel cells. Moreover, sewage sludge can be assumed as an alternative renewable energy source to the fossil fuels, and the environmental pollution originating from the disposal of sewage sludge can be partially reduced. (C) 2002 International Association for Hydrogen Energy. Published by Elsevier Science Ltd. All rights reserved.