Hydrogen was produced in a biotrickling filter (BF) packed with perlite and fed with oat straw acid hydrolysate at 30 degrees C. Inlet chemical oxygen demand (COD) from 1.2 to 35 g/L and hydraulic retention time (HRT) between 24 h and 6 h were assayed. With increasing inlet COD or decreasing HRT, H(2) production rate (HPR) increased but H(2) production yield (HY) decreased. Maximum HPR of 81.4 mL H(2)/L(reactor) h (3.3 mmol H(2)/L(reactor) h) and HY of 2.9 mol H(2)/mol(hexose consumed) were found at an inlet COD of 0.05 g(COD)/L h (HRT 24 h) and 2.9 g(COD)/L h (HRT 12 h), respectively. Maximum hydrogen composition in gas was 45 +/- 4% (v/v) with CO(2) as balance. Methane was not detected. Maximum HPR and inlet COD used in this work were higher than others reported for reactors with suspended or fixed biomass. However, implementation of strategies for biomass control to avoid reactor clogging is needed. Copyright (C) 2010, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.