Aspergillus fumigatus IMI 255091 has been found to grow well on ground straw as the principal substrate, Production of β - d -glucosidase ( β - d -glucoside glucohydrolase, EC 3.2.1.21), endo-1,4- β - d -glucanase [1,4-(1,3;1,4)- β - d -glucan 4-glucanohydrolase, EC 3.2.1.4] and d -xylanase (1,4- β - d -xylan xylanohydrolase, EC 3.2.1.8) was maximal within 7 days with 4% (w/v) straw. Comparisons were made with both a conventional agitated fermenter and an air-lift fermenter. The latter gave the highest yields. The β - d -glucosidase was partially purified by fractionation and its K m determined. This was found to differ from that of other β - d -glucosidases reported in the literature.