Growth of a wild sb ain of Schizophyllum commune on cellulose or cellulose-rich substrates in submerged culture resulted in the production of cellulase xylanase, and mannanase activities. Pure xylan or galactomannan as carbon sources did not specifically induce the formation of xylanase or mannanase, respectively. Production of cellulase, xylanase, and mannanase activities decreased with an increasing ratio of xylan to cellulose or mannan to cellulose, in the growth medium. During growth experiments, formation of xylanase, cellulase as well as mannanase was induced not only by cellulose, but also by cellobiose, lactose, and L-sorbose. Xylans from birchwood xylose, and beta-methyl-D-xyloside, a structural analogue of xylobiose, did nor induce xylanase formation when employed as substrates. These results indicate that the synthesis of xylanase, cellulase and mannanase activities is likely to be under common regulatory control in the case of Schizophyllum commune. The inducer seems to be a small molecule derived from cellulose. Constitutive levels of xylanase and cellulase activities were detected during growth of the fungus on easily metabolizable substrates such as glucose, xylose, or glycerol. Among various organic nitrogen sources tested yeast extract was found to be optimal for the production of xylanase.