A beta-mannosidase was purified from Phlebia radiata grown in a medium containing wheat bran or galactomannan as a carbon source. Maximal activity was observed at pH 5.5 and at 50 degrees C. Highly purified isoforms of beta-mannosidase (GM-1, GM-2) isolated from media containing galactomanan and (OT-1) media with wheat bran were obtained by means of column chromatography on Q-Sepharose, SP-Sepharose and chromatofocusing on Polybuffer Exchanger PBE-94.