Production of xylanases by eight Thermomyces lanuginosus strains was examined on bagasse pulp under solid state fermentation (SSF). The optimum pH and moisture content for xylanase production by SSF was 7.0 and 83%, respectively. Time course experiments indicated maximum xylanase production after 4 days. The most efficient producer of xylanase was T lanuginosus ATCC 46882 with 5098 U xylanase/g bagasse pulp. The crude SSF enzymes displayed varying degrees of bleach enhancing ability on bagasse pulp depending on the microbial source and enzyme dose. The crude SSF enzymes of T lanuginosus ATCC 36350 appeared as most efficient in biobleaching improving the final brightness by 2 points over control. At the same bleaching efficiency, the SSF xylanase of this strain was up to 33% more cost-efficient than a commercial xylanase preparation. Reductions in the chlorine consumption of up to 30% were possible with the SSF xylanases of T lanuginosus ATCC 36350 and ATCC 46882. It was demonstrated that the direct use of in situ SSF enzymes can benefit the bleaching process to lower the xylanase production costs and improve the economics and viability of the biobleaching technology. To the best of our knowledge, this is the first report on the application of SSF xylanase to enhance the bleachability of bagasse soda pulp. (c) 2005 Elsevier Ltd. All rights reserved.