Background Advances on enzyme technology have improved the economics of cellulosic ethanol. Nevertheless, there is still great interest to improve the production and the characteristics of the enzymatic preparations. One possibility to reduce the cost of the enzymes is on-site enzyme production in a biorefinery plant, in which part of the lignocellulosic material already available can be used as a cheap carbon source in the enzyme production. Results Steam exploded wheat straw at two different severity conditions was evaluated as carbon source for enzyme production by Trichoderma reesei. The results showed that volumetric production of cellulases and -glucosidase increased when using a carbon source with high cellulose content. When a carbon source with a higher content of hemicellulose was used the enzymatic mixture showed significantly higher proportions of hemicellulase activities (xylanase, -xylosidase and -L-arabinofuranosidase), which had a positive effect on subsequent enzymatic hydrolysis. Conclusions The proportion of cellulose and hemicellulose in the carbon source has an influence on the composition of the enzymatic cocktail. The higher the cellulose and hemicellulose content, the higher the titer of cellulase and hemicellulase produced by the fungus, respectively. The enzyme preparations with higher hemicellulase activities were more efficient in hydrolyzing xylan-containing substrates. (c) 2012 Society of Chemical Industry.