In biohydrogen producing processes, cumulative gaseous end products can cause negative effects on hydrogen production. This study investigated inhibitory effects of hydrogen and carbon dioxide on biohydrogen production behavior of moderately thermophile Thermoanaerobacterium thermosaccharolyticum W16 with glucose or xylose as the carbon source. Experimental results indicated that high hydrogen partial pressure largely decreased the hydrogen yield by 16.9% and 18.8% for glucose and xylose respectively (from 2.07 to 1.72 mol H(2)/mol glucose and from 1.80 to 1.46 mol H(2)/mol xylose). Under high carbon dioxide partial pressure, the hydrogen yield was slightly dropped by 6.8% and 5.6% to 1.93 mol H(2)/mol glucose and 1.70 mol H(2)/mol xylose respectively. H(2) production rate, cell growth, and liquid end components were also affected by varied gaseous components, which led to the shifts of metabolic pathways and corresponding NADH flows due to gaseous feedback inhibition. Transcription levels of functional [FeFe] hydrogenases, which were determined by quantitative reverse transcription-polymerase chain reaction (qRT-PCR), performed corresponding susceptibilities under high hydrogen and carbon dioxide partial pressures. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.