Exo-polymer (EP) was produced at 1.2 g 1(-1) in submerged culture of Auricular auricula judge. Crude EP (AJ-0) has 70% anti-complementary activity (inhibition of total complementary hemolysis 50%; ITCH50). The activating pathway of the complement system occurred through both the classical and alternative pathways, though the major pathway was the classical one. Fractionation of AJ-0 using Sepharose CL-6B gel chromatography gave three major fractions (AJ-Fr-I, II and III) of which the first was the most active. The mycelial growth and EP production of A. auricula judge were optimal at pH 6, 25degreesC and pH 5, 25degreesC, respectively.