An extracellular proteolytic enzyme was produced by Conidiobolus lamprauges accompanied with chitin-binding hemagglutinin. The protease was partially purified by ammonium sulfate precipitation and CM Sephadex, concanavalin A-Sepharose, and Sephadex G-75 chromatographies. The molecular weight was estimated to be about 20, 000 by gel filtration. Agglutination of human erythrocytes by C. lamprauges agglutinin, wheat germ agglutinin, soy bean agglutinin and concanavaline A was accelerated by treating erythrocytes with this enzyme, whereas agglutination by Streptomyces L-fucose-specific lectin was not affected. Agglutination by Vibrio was repressed. Sodium dodecyl sulfate polyacrylamide gel electrophoresis of the erythrocyte membrane preparations from digested cells showed that this protease and pronase hydrolyzed "Band 3" and sialoglycoproteins [Fairbanks et al., Biochemistry, 10, 2606 (1971)] whereas papain and trypsin hydrolyzed only the latter. The relationships between these membrane proteins and the receptors for hemagglutinins were discussed.