When grown on wheat bran as the only carbon source, the filamentous fungus Talaromyces thermophilus produces large amounts of beta-xylosidase activity. The presence of glucose drastically decreases the beta-xylosidase production level. The beta-xylosidase of T. thermophilus was purified by ammonium sulfate precipitation, DEAE-cellulose chromatography, and gel filtration (high-performance liquid chromatography). The molecular mass of the enzyme was estimated to be 97 kDa by sodium dodecyl sulfate polyacrylamide gel electrophoresis and gel filtration. The enzyme activity was optimum at 50 degrees C and pH 7. The apparent Michaelis constant K-m of the beta-xylosidase was 2.37 mM for p-nitrophenyl-beta-D-xylopyranoside, with a V-max of 0.049 mu mol min(-1) per milligram protein. Enzyme activity was inhibited by Cu2+, Hg2+, and Zn2+ and activated by Ca2+, Mn2+, and Co+ at a concentration of 5 mM. At high xylose concentration, this enzyme catalyses the condensation reaction leading to xylobiose production.