Hydrolysates resulting from the lignocellulosic biomass pretreatment in bioethanol production may be used to produce biogas. Such hydrolysates are rich in xylose but also contain lignin polymers or oligomers as well as phenolic and furan compounds, such as syringaldehyde, vanillin, HMF, furfural. The aim of this study was to investigate the impact of these byproducts on biomethane production from xylose. The anaerobic digestion of the byproducts alone was also investigated. No inhibition of the anaerobic digestion of xylose was observed and methane was obtained from furans: 430 mL CH4/g of furfural and 450 mL CH4/g of HMF; from phenolic compounds: 453 mL CH4/g of syringaldehyde and 105 mL CH4/g of vanillin; and, to a lesser extent, from lignin polymers: from 14 to 46 mL CH4/g MV. The use of different natural polymers (lignosulfonates, organosolv and kraft lignins) and synthetic dehydrogenative polymers showed that higher S/G ratios and lower molecular weights in lignin polymers led to greater methane production. (C) 2011 Elsevier Ltd. All rights reserved.