An autolysis chitinase was purified from the cultural medium of the anaerobic fungus Piromyces communis OTS I by ammonium sulfate precipitation, affinity chromatography with regenerated chitin, chromate-focusing, gel filtration, and chromato-focusing again. The optimal pH and temperature were 6.0 and 50 degrees C, respectively, for a 20-min assay. The chitinase was stable from pH 6.0 to 8.0, but was unstable at 70 degrees C for 20 min, The molecular mass of chitinase was estimated by SDS-PAGE to be 44.9 kDa, and its pi was 4.4. The enzyme activity, which was of the 'endo' type, was inhibited by Hg2+ and allosamidin. The chitinase hydrolyzes chitin powder and fungal cell walls at a higher rate than an artificial chitin substrate. It can be concluded that extracellular chitinase is similar to cytosolic chitinase, but they are not the same protein.