In a recent screening for thermophilic bacteria from Azores hot springs, a Bacillus sp strain 3M, exhibiting cellulase-free extracellular xylanolitic activity, was isolated. Further enzyme characterization from liquid cultures grown on birchwood xylan revealed that the endo-1,4-beta-xylanase retains 100% of activity for at least 3 d at 55 degrees C. At 80 degrees C, it retains 47% of its maximal activity, and the enzyme is still active at 90 degrees C. The optimum pH of the enzyme has a broad pH range, between 6.0 and 7.5, and it is remarkably active for the alkaline region, exhibiting 89% of relative activity at pH 9.0. The enzyme was partially inactivated by different divalent metal ions. Because of its tolerance for high temperature and pH conditions, and the absence of contaminating cellulase activity, the xylanase produced by Bacillus sp 3M appears to be attractive for use in the pulp and paper industry. Indeed, the efficiency of the enzyme application to the kraft Eucalyptus pulp was studied for bleaching pretreatment, resulting in a moderate increase of pulp bleachability.