Ultrahigh hydrostatic pressure (UHP) was applied to enhance the enzymatic hydrolysis of xylan in cellulosic fibers. The pretreatment improved xylan accessibility in the fiber cell wall and a 5-10-fold increase in the initial hydrolysis rate of xylan by xylanase was observed when Eucalyptus globulus kraft bleached pulp was pretreated at hydrostatic pressures of 300-400 MPa for 15-45 min. The rate and the extent of hydrolysis can be controlled by varying the pressure and the exposure time of UHP treatment prior to enzymatic hydrolysis. Sequential UHP pretreatment and hydrolysis by xylanase disaggregated the hydrated cellulose fibrils and led to the gelation of cell wall regions accessible to enzymatic attack. UHP could therefore become a tool for the engineering of enzymatic reactions within cellulosic fibers to obtain products with tailored properties. (C) 2011 Elsevier Ltd. All rights reserved.