The extracellular xylanases produced by recombinant Escherichia coli carrying the 4,5-kb DNA fragment from an alkaliphilic thermophilic Bacillus (NCIM 59) were purified to homogeneity. The M(r) of the enzymes were estimated to be 35,000 (xylanase I) and 14,500 (xylanase II) by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The purified xylanases had similar temperature (60 degrees C) and pH (6) optima, and the isoelectric points were 4 and 8, respectively. The enzymes retained 100% activity at 50 degrees C for 24 h; however, at 60 degrees C they showed a half-life of 2 h The apparent K-m values of xylanase I and II were 5.8 and 8.3 mg ml(-1) and V-max values were 0.010 and 0.520 mu mol min(-1) mg(-1), respectively. The recombinant xylanases showed reduced ability to bind xylan and had lower specific activity and K-m values than those of the xylanases from the parent Bacillus reported previously. Both enzymes yielded different hydrolysis patterns when incubated with oat spelt xylan. The hydrolysis pattern of the recombinant xylanases was found to be distinctly different from that of the original xylanases, which may be due to differential binding of the cloned enzymes to the substrate.