An alkaliphilic, moderately thermophilic and halophilic bacterial isolate capable of producing a high titer of extracellular thermo-alkali-stable, cellulase-free endoxylanase was isolated from the paper mill effluents. It was identified as Bacillus halodurans. The purified xylanase was active from pH 7 to 12 and 30 to 100 degrees C with optimal activity at pH 9.0 and 80 degrees C. It had T(1/2) values of 40 and 15 min at 70 and 80 degrees C, respectively. Activity was stimulated by dithiothreitol but strongly inhibited by N-bromosuccinimide. Its action on birchwood xylan and agroresidues liberated xylooligosaccharides of 2-7 degree of polymerization, and thus, the mode of action is similar to endoxylanases of the family 10 glucoside hydrolases.