This study evaluated the use of two types of substrates, glucose and sucrose, feeding an anaerobic fixed-bed bioreactor. The biogas produced was composed of H-2 and CO2, without methane. Maximum hydrogen yields were 3.22 mol H-2 mol(-1) sucrose(converted) and 1.51 mol H-2 mol(-1) glucose(converted). The main intermediates were acetic acid, butyric acid, and ethanol. The greatest difference, however, was in the stability of the process. The operation of the reactor with sucrose exhibited a drop in biogas production, whereas operation with glucose was stable after a slight decrease in biogas production. This decrease may have been caused by the differential growth of microbial populations in each reactor, namely, the growth of organisms that use the Wood-Ljungdahl metabolic pathway. Copyright (C) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.