HPLC, SEM and XRD techniques have been proposed as methods for ascertaining the changes occurring in polysaccharides (cellulose and xylans) and fibres during the xylanase bleaching processes. TCF and ECF bleached pulps with and without enzyme pretreatment were analysed. The ratio of carbohydrates present in the pulp, observation of changes occurring in the surface of the fibres and the crystallinity and accessibility of the bleached fibres were determinated. These characteristics have been related with pulp properties. Xylan content decreased when Pulp was bleached. Xylanase treatment substantially reduced the xylose content present in pulp, measured by HPLC after the hydrolysis method of the sample. Morphological changes in the fibres occurred when the enzymatic treatment was applied. Bleaching increased the crystallinity of the pulp and enzyme pretreatment also affected the crystallinity of cellulose fibres. (C) 2004 Elsevier Ltd. All rights reserved.