A novel endoglucanase active on 1,3-1,4-beta -D-glucans was purified to apparent homogeneity from submerged cultures of the moderately thermophilic aerobic fungus Talaromyces emersonii CBS 814.70. The enzyme is a single subunit glycoprotein with M-r and pI values of 40.7 +/- 0.3 kDa and 4.4, respectively, and an estimated carbohydrate content of 77% (w/w). The purified beta -glucanase displayed activity over broad ranges of pH and temperature, yielding respective optima values of pH 4.8 and 80 degreesC. This enzyme was markedly thermostable with 15% of the original activity remaining after incubation for 15 min at 100 degreesC. Substrate specificity studies revealed the identity of the enzyme to be a 1,3-1,4-beta -D-glucanase. Identical K-m values (13.38 mg.ml(-1)) were obtained with lichenan and BEG, while the V-max value with lichenan (142.9 IU.mg(-1)) was approximately twice the value obtained with BEG (79.3 IU.mg(-1)). Time-course hydrolysis of barley-beta -glucan did not proceed linearly with respect to time indicating an 'endo' or more processive action for the enzyme. HPAEC fractionation of the products of hydrolysis yielded a range of oligosaccharides, with cellobiose, cellotriose and cellotetraose being the predominant oligosaccharide products.