Two xylanases from Bacillus firmus were purified to homogeneity by gel filtration and ion-exchange chromatography, These enzymes have molecular weights of 45 kDa and 23 kDa, respectively, and both show enzymatic activity over the pH range of 5.0-11.0 at 37degreesC. These enzymes hydrolyzed xylan from birchwood to release mainly the products of xylose, xylotriose and xylohexose. thus indicating that the xylanases act preferentially toward the internal glycosidic bonds of xylo-oligosaccharides. However, the two xylanases show different modes of action. and a combination of both is likely to lead to concerted degradation of xylan down to the mono- and disaccharides.