Quercetin was the best inducer for the production of a highly glucose-tolerant, extracellular beta-glucosidase in Aspergillus niger and Aspergillus oryzae. The enzyme was separated from the major and common beta-glucosidase by gel filtration and that from Aspergillus oryzae further purified by ion-exchange chromatography. It was highly resistant to glucose inhibition (K-i = 953 mM), had a pI of 4.2, optimum pH of 4.5-6.0 and a molecular mass of 30 kDa according to gel filtration. The enzyme was active against cellobiose and alkyl glucosides.