Nine Trichoderma harzianum strains were screened for beta-xylosidase activity when grown in solid-state cultures on media containing wheat bran as the carbon source. All strains produced beta-xylosidase activity, the most active being in extracts of cultures of T. harzianum strain 4. A beta-xylosidase was purified by ammonium sulfate precipitation, ultrafiltration, gel filtration, and ion exchange chromatography from solid-state cultures of T. harzianum strain C. Enzyme preparations yielded a single band when stained for protein following eletrophoresis. The molecular weight value, calculated following SDS-PAGE, was determined to be 60 kDa. beta-Xylosidase was most active at pH 4.0-4.5 and 70 degrees C. This enzyme had a K-m value of 0.053 mM. The phenol-sulfuric acid method detected the presence of a small amount of carbohydrate in the purified enzyme preparation. beta-Xylosidase was active against some p-nitrophenylglycosides. The enzyme was inactive against xylan and PNPG. beta-xylosidase activity was inhibited by xylose and SDS. Iodoacetamide, dithiothreitol, gluconolactone, glucose, and mercuric chloride failed to inactivate this enzyme's activity. A synergistic effect was observed when beta-xylosidase from T. harzianum strain C and beta-xylanase from Aspergillus fumigatus were incubated with pretreated arabinoxylan.