The cost and hydrolytic efficiency of enzymes are major factors that restrict the commercialization of the bioethanol production process from lignocellulosic biomass. Hemicellulases and other accessory enzymes are becoming crucial to increase enzymatic hydrolysis (EH) yields at low cellulase dosages. The aim of this work was to evaluate the effect of two recombinant hemicellulolytic enzymes on the EH of steam pretreated wheat straw. Pretreatments at two severity conditions were performed and the whole slurry obtained after steam explosion pretreatment was employed as substrate. An endoxylanase (Xln C) from Aspergillus nidulans and an (x-L-arabinofuranosidase (AF) from Aspergillus niger, have been applied in combination with cellulase enzymes. A degree of synergism of 29.5% and increases up to 10% in the EH yields were obtained, showing the potential of accessory activities to improve the EH step and make the whole process more effective. (C) 2011 Elsevier Ltd. All rights reserved.