A locally isolated strain of Aspergillus niger van Tieghem was found to produce thermostable beta-xylosidase activity. The enzyme was purified by cation and anion exchange and hydrophobic interaction chromatography. Maximum activity was observed at 70-75 degrees C and pH 4.5. The enzyme was found to be thermostable retaining 91 and 87% of its original activity after incubation for 72 h at 60 and 65 degrees C, respectively, with 52% residual activity detected after 18 h at 70 degrees C. Available data indicates that the purified beta-xylosidase is more thermostable over industrially relevant prolonged periods at high temperature than those reported from other A. niger strains. Maximum activity was observed on p-nitrophenyl-beta-D-xylopyranoside and the enzyme also hydrolysed p-nitrophenyl beta-D-glucopyranoside and p-nitrophenyl alpha-L-arabinofuranoside. The purified enzyme acted synergistically with A. niger endo-1,4-beta-xylanase in the hydrolysis of beechwood xylan at 65 degrees C. During hydrolysis of pretreated straw lignocellulose at 70 degrees C using a commercial lignocellulosic enzyme cocktail, inclusion of the purified enzyme resulted in a 19-fold increase in the amount of xylose produced after 6 h. The results observed indicate potential suitability for industrial application in the production of lignocellulosic bioethanol where thermostable beta-xylosidase activity is of growing interest to maximise the enzymatic hydrolysis of lignocellulose.