The effects of furans (furfural and 5-hydroxymethylfurfural (HMF)) on hydrogen (H-2) production using mixed anaerobic cultures were evaluated by conducting batch experiments. Two mixed anaerobic cultures (culture A and B) fed furans plus glucose and treated with and without linoleic acid (LA) at pH 5.5 were maintained at 37 degrees C. In the LA inhibited cultures A and B fed 0.75 g L-1 furfural and 0.25 g L-1 HMF, the maximum H-2 yields observed were 1.89 +/- 0.27 mol mol(-1) glucose and 1.75 +/- 0.22 mol mol(-1) glucose, respectively. In cultures with maximum H-2 yields, Clostridium sp. and Flavobacterium sp. were dominant. Acetate, butyrate and ethanol were the major soluble metabolites detected in cultures A and B whereas propionate was also dominant in culture B. A canonical correspondence analysis based on the byproducts and the relative abundance of the terminal-restriction fragments revealed less variation between cultures treated with LA and low correlation value between the factors and the species composition. Copyright (C) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.