Xylanase T-6 is a thermostable alkaline-tolerant enzyme that is produced by Bacillus stearothermophilus T-6. Xylanase T-6 was found to bleach pulp effectively at pH 9 and 65 degrees C and was used successfully on an industrial-scale mill trial. To facilitate the future characterization of the protein via X-ray analysis and protein engineering, it was necessary to overexpress the enzyme in Escherichia coli. The xylanase gene was cloned into T-7 polymerase expression vectors and its expression was optimized. The enzyme was found to constitute over 70% of the cell protein and it was efficiently purified from the host proteins by a single heating step. Over 2 g soluble and active enzyme per 1 culture were achieved.