Two extracellular proteolytic activities from the wood degrading fungus Aspergillus terreus have been characterized. Proteinase I (serine thiol-dependent enzyme) was active over a broad pH range (7.0-10.0) and at 55 degrees C. The second proteinase (metalloproteinase) showed optimal activity at pH 6.0-7.0 and at 65-70 degrees C. Both proteins had isoelectric points at acid pH and contained carbohydrate moieties. The metalloproteinase possessed a uniquely high content of serine and threonine and an extremely low percentage of glutamate and aspartate. The metalloproteinase was involved in the formation of the low molecular mass endoglucanases of A. terreus.