This study evaluated the impact of furfural (a furan derivative) on hydrogen production rates and yields at initial substrate-to-microorganism ratios (S degrees/X degrees) of 4, 2, 1, and 0.5 gCOD/gVSS and furfural concentrations of 4, 2, 1, and 0.5 g/L. Fermentation studies were carried out in batches using synthetic lignocellulosic hydrolysate as substrate and mesophilic anaerobic digester sludge as seed. Contrary to other literature studies where furfural was inhibitory, this study showed that furfural concentrations of up to 1 g/L enhanced hydrogen production with yields as high as 19% from the control (batch without furfural). Plots of hydrogen yields against g furfural/g sugars and hydrogen yields versus g furfural/g biomass showed negative linear correlation indicating that these parameters influence biohydrogen production. Regression analysis indicated that g furfural/g sugars(initial) exerted a greater effect on the degree of inhibition of hydrogen production than g furfural/g VSSfinal. (C) 2016 Elsevier Ltd. All rights reserved.