The cloning, sequencing, and expression in E. coli of a gene from the hyperthermophile, Thermatoga maritima, encoding a thermostable xylanase is reported The enzyme is active at 100 degrees C for several hours and efficient in releasing lignin from kraft pulp. Comparison of the T. maritima recombinant enzyme with a commercially available xylanase, Pulpzyme, indicated that the hyperthermophilic enzyme has several advantages that make it an attractive biotechnological reagent. In studies of the release of reducing sugars and lignin from hardwood and softwood kraft pulp, the specific activity for the partially purified enzyme was 131 U mg(-1). The enzyme released reducing sugars and aromatic materials from the pulp suspensions over a pH range from 3.5-10.