Soaking in aqueous ammonia (SSA) and/or xylanase pretreatments were developed on wheat straw. Both pretreatments were conducted at high-solids conditions: 15% and 20%, respectively, for SSA and xylanase pretreatments. SSA pretreament led to the solubilisation of 38%, 12% and 11% of acid insoluble lignin, xylan and glucan, respectively. In case of xylanase pretreatment, 20% of xylan were removed from native wheat straw. When pretreatments were applied consecutively (SSA and xylanase) on straw, 56% of xylans were hydrolysed and a rapid reduction of media viscosity occurred. The enzymatic hydrolysis of cellulose with cellulases was evaluated from the different combinations of pretreated wheat straw. Cellulose hydrolysis was improved by 2.1, 2.2 and 2.9, respectively, for xylanase, SSA and SSA/xylanase pretreated straw. Xylans from untreated and pretreated wheat straws were also solubilised with cellulases. Chemical analysis of pretreated straw residues in connection with yields of cellulose hydrolysis highlighted the role of phenolic acids, acetyl content and cellulose crystallinity for cellulase efficiency. (C) 2010 Elsevier Ltd. All rights reserved.