In biochemical process industries, the dynamic environment within the bioreactor and in the purification equipment is known to affect the enzyme activity and yield of enzyme production. This has drawn our attention to examine the effect of various flow parameters on the deactivation behavior of enzyme in stirred tank reactor. In the present work, cellulase deactivation was investigated in 0.1, 0.3 and 0.57 m W. stir-red vessels with single and dual impeller. Enzyme solution was subjected to hydrodynamic stress using various types of impeller and impeller combinations over a wide range of power consumption (0.02 < P/V < 12.56 kW/m(3)). The effects of tank diameter, impeller diameter, blade width, blade angle and number of blades were studied on the extent of deactivation. The results have been compared with the previously published literature. Attempts have been made to relate the extent of deactivation with the flow pattern (maximum and average value of turbulent energy dissipation rate, average shear rate and average turbulent normal stress). The extent of cellulase deactivation has been found to correlate well with the average turbulent normal stress within the stirred vessel. (C) 2004 Elsevier Ltd. All rights reserved.