Unbleached bagasse soda pulp was pretreated with a purified xylanase from Thermomyces lanuginosus SSBP under optimum conditions using various enzyme charges. The xylanase exhibited direct brightening abilities on bagasse pulp improving brightness by 1.5 points, however, kappa number decreased by 0.5 points. The purified enzyme, used at 150 U/g, enhanced brightness of DED-bleached pulp by 4.5 points whereas pretreatment at a charge of 5 U/g pulp brightened pulp by 2.6 points over control, indicating the high enzyme efficiency at low doses. No correlation between kappa number and brightness was observed during biobleaching. Chlorine dioxide consumption was reduced by 18% with xylanase-pretreated pulps while still maintaining brightness at the control level. Examination of pulp strength properties revealed negligible differences between the enzyme treated and control samples. Scanning electron microscopy revealed significant surface modification of bagasse pulp fibres without marked fibre disruptions. (C) 2002 Elsevier Science Ltd. All rights reserved.