A membrane-bound chitinase from cell wall fractions of the anaerobic ruminal fungus, Piromyces communis OTS1, was purified by affinity chromatography, gel filtration, and chromatofocusing. The molecular size of the chitinase was estimated by gel filtration to be 42.4 kDa and by SDS-PAGE to be 44.8 kDa, and its pI was 4.4. Activity was inhibited by Hg2+ and allosamidin. The activity at 39 degrees C was greatest at pH 6.0. It had an 'endo' type action. Solubilization tests indicated that plasmalemma-bound chitinase was held in place by an electrostatic type interaction. Characterization of the membrane-bound chitinase was more similar to that of extracellular chitinase than cytosolic chitinase. This suggested that membrane-bound chitinase was the origin of extracellular chitinase.