The process of bioconverting lignocellulosic materials into ethanol in the simultaneous saccharification and fermentation system depends upon the activity of Penicillium decumbens cellulase. The influence of both ethanol and the yeast on this cellulase activity has been studied and it has been found that ethanol in concentrations between 1% and 7% inhibits the enzymatic hydrolysis of crystalline cellulose but the inhibition is reversible. At ethanol concentrations between 1% and 9%, the activity of beta-glucosidase increases with increasing ethanol concentration. Yeast has no effect on the enzymatic activity. (c) 2006 Elsevier Inc. All rights reserved.