Production of exocellular β-mannan- and xylan-degrading enzymes by eight wood rotting fungi was studied. Although all organisms excreted β-mannanase, endoxyfanase and acetylxylan esterase, production ofL-α-arabinosidase and 4-O-methylglucuronidase was variable. β-Mannanosidase was not detected in any culture filltrate. Righest β-mannanase and endoxylanase activities were observed in cultures ofPolyporus versicolor andSchizophyllum commune grown in Avicel-supplemented media. While crude β-mannanases fromLinzites saepiria andS. commune exhibited equivalent affinities for gluco- and galactomannan substrates,P. versicolor β-mannanase preferred a glucomannan substrate and did not use galactomannan from guar sum as a substrate.