The paper reports the multiplicity of xylanase in a newly isolated thermophilic fungus Myceliophthora sp. IMI 387099. The expression of different xylanase isoforms and level was found to be dependent on substrate type, as well as culture conditions. The zymograms developed from proteins resolved on PAGE and IEF showed rice straw as the best inducer. Of the 10 xylanases produced in presence of rice straw, the major xylanases were of acidic pI. Each of the 10 xylanases was functionally diverse and showed different specificity and catalytic activity against a variety of substituted/unsubstituted xylan and aryl substituted substrates. The major acidic xylanases showed no preferential activity towards xylan (substituted/unsubstituted), however, the basic and moderately acidic xylanases showed higher activities towards substituted xylans (LWX, RAX, WAX). (C) 2004 Elsevier Inc. All rights reserved.