Products of hemicellulose hydrolysis, particularly xylo-oligosaccharides, are inhibitory to cellulose hydrolysis by cellulase enzymes.  Xylose causes greater inhibition of cellulases than xylan, but is less inhibitory than soluble xylo-oligomers.  Arabinose may be inhibitory to β-glucosidases as well.  While β-glucosidase in Novozyme 188 may moderate the inhibition of cellulase by cellobiose through the hydrolysis of the cellobiose to glucose, other hydrolytic activities found in this enzyme preparation may also release other inhibitors of cellulolytic enzymes.  To further investigate this phenomenon, we used untreated and liquid hot water pretreated corn stover to test the effects of  the combined action of Spezyme CP and a purified Aspergillus niger β-glucosidase.  The results were compared to the combined action of the cellulase and Novozyme 188 or purified hemicellulases (xylanase and α-arabinofuranosidases).  The results obtained show inhibitory effects may be promoted  by the presence of Novozyme 188, and that the inhibition increases progressively when hemicellulases, and particularly xylanase and α-arabinofuranosidases are added to the enzyme mixture in increasing amounts.  This work shows confirms that inhibition is a complex phenomenon  defined not only by the properties of corn stover but more importantly the properties and activities found in  β-glucosidase preparations.