The xyn10B gene, encoding the endo-1,4-beta-xylanase Xyn10B from Thermotoga thermarum, was cloned and expressed in Escherichia coli. The ORF of the xyn10B was 1,095 bp and encoded to mature peptide of 344 amino acids with a calculated MW of 40,531 Da. The recombinant xylanase was optimally active at 80 A degrees C, pH 6.0 and retained approx. 60 % of its activity after 2 h at 75 A degrees C. Apparent K (m) , k (cat) and k (cat) /K (m) values of the xylanase for beechwood xylan were 1.8 mg ml(-1), 520 s(-1) and 289 ml mg(-1) s(-1), respectively. The end products of the hydrolysis of beechwood xylan were mainly oligosaccharides but without xylose after 2 h hydrolysis.