Batch experiments were carried out to study the effects of acid (HCl) and alkaline (NaOH) pretreatments on saccharification of grass and subsequent microbial hydrogen production at 35 degrees C and initial pH 7.0. Liquid metabolites and hydrogen production characteristics were also studied. Results show that the saccharification efficiency and hydrogen production from grass pretreated by acid and alkali were higher than those from unpretreated grass and that acid pretreatment was better than alkaline pretreatment for enhancing the hydrogen yield from grass. A maximum cumulative hydrogen yield of 72.21 mL/g-dry grass was achieved from substrate pretreated with 4% HCl, which was 16.45-fold greater than that from untreated substrate. Only H-2 and CO2 were present in the biogas. The main liquid metabolite found after fermentation was acetic acid. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.