Composition, stability at different pH and temperatures and hydrolytic efficiency toward microcrystalline cellulose (MCC) of Penicillium cellulase were evaluated. The pH optimum (4.5-5.0) of filter paper activity (FPA) and temperature optimum (50-55 degrees C) were determined. Maximum stability of FPA was observed at pH 4.0-5.0 and temperature 40-50 degrees C. A minor contribution of stirring (3-4%) in inactivation of Penicillium preparation was shown. Kinetic parameters of MCC hydrolysis by Penicillium cellulase were determined at optimal conditions (pH 4.5, 50 degrees C): K-m=50 g/l, V-max=330 mu M/min per gram of protein. More effective saccharification of MCC by Penicillium preparations compared to Trichoderma reesei cellulases with the same level of total cellulolytic activity (FPA=1.0 U/ml) was demonstrated. Glucose concentration in 24 h hydrolysate was 41 g/l for Penicillium cellulase, 15 g/l for T. reesei (Privolzhski Fermentation Plant) and 26 g/l for T. reesei (Genencor). Hydrolysates of Penicillum cellulase contained only 9% of cellobiose compared to 24-40% of cellobiose for T. reesei cellulases. Factors contributing to superior properties of Penicillium cellulase - higher level of cellobiase activity and higher operational stability - are discussed.