Hydrogen and methane were produced from wastewater sludge using a clostridium strain. The original sludge and pre-treated (acidified, basified and freeze/thawed) sludges were the testing samples. Some pre-treatments enhanced hydrogen yield, whereas other treatments enhanced methane yield. Hydrogen fermentation can be used as a pre-stage to improve subsequent methane production from wastewater sludge. (C) 2006 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.