Leaves are one of the main by-products of forestry. In this study, batch experiments were carried out to convert poplar leaves pretreated by different methods into hydrogen using anaerobic mixed bacteria at 35 degrees C. The effects of acid (HCl), alkaline (NaOH) and enzymatic (Viscozyme L, a mixture of arabanase, cellulase, beta-glucanase, hemicellulase and xylanase) pretreatments on the saccharification of poplar leaves were studied. Furthermore, the effects of acid and enzymatic pretreatment on hydrogen production, together with their corresponding degradation efficiencies for the total reducing sugar (TRS) and metabolites were compared. A maximum cumulative hydrogen yield of 44.92 mL/g-dry poplar leaves was achieved from substrate pretreated with 2% Vicozyme L, which was approximately 3-fold greater than that in raw substrate and 1.34-fold greater than that from substrate pretreated with 4% HCl. The results show that enzymatic pretreatment is an effective method for enhancing the hydrogen yield from poplar leaves. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.