A thermostable carboxymethyl cellulase (CMCase) was purified to homogeneity from a wheat bran culture of the thermophilic fungus Sporotrichum sp. HG-1, an isolate from a compost heap. The enzyme had a molecular weight (M-r) of 33,000 by SDS-PAGE. The optimum temperature and pH for enzyme activity were 70 degrees C and 4.5-5.0, and the enzyme was heat stable. Uncooked Thai rice was digested so as to cause its disintegration by the addition of purified CMCase, but not by the addition of xylanase purified from strain HG-1. Ferulic acid conjugated to oligosaccharide was released significantly by the combined action of CMCase and xylanase, but the free form of ferulic acid was not detectable.