The degradation capacity of extracellular enzyme preparations from two anaerobic fungi, i.e., Piromyces sp. strain E2 and Neocallimastix patriciarum strain N2, toward several types of lignocellulosic substrates was studied. The enzymes were capable of effectively converting up to 2% (w/v) microcrystalline cellulose (Avicel) to glucose, thereby indicating the presence of all catalytic activities (endoglucanases, exoglucanases, and beta-glucosidases) needed. Performance of these enzymes surpassed that of a combined preparation of the commercial enzymes Celluclast and Novozym in batch degradation of 2% (w/v) Avicel. The enzymes from anaerobic fungi are very stable at 40 degrees C. After one week of incubation at this temperature in the absence of substrate, about 50% of activity towards Avicel was retained. Although the performance of the enzyme system was lowered when increasing initial glucose concentrations were applied, still over 30% of sugar release was observed at an initial monomer concentration of 200 mM. Various natural lignocellulosic materials were ground and tested as substrates. A negative correlation was found between the amount of lignin in the substrate and the release of soluble sugars.