Mutagenesis of Fusarium oxysporum DSM 841 enhanced the activity of xylanase and beta-xylosidase enzymes by more than threefold. Wild-strain spores were subjected to UV or N-methyl-N’-nitro-N-nitrosoguanidine treatments. The hyperxylanolytic mutant (NTG-19) secretes high levels of xylanolytic enzymes on commercial xylan as well as several agricultural residues, of which wheat bran supported maximum enzyme yields. Addition of 0.2% olive oil, an inexpensive source of fatty acids, resulted in a further 25% increase in enzyme secretion.