Lysozyme (alpha-helix dominant structure) and pepsin (beta-sheet dominant structure) were exposed to microsecond pulsed electric field (PEF) at 3.5 x 10(6) V/m. The response of enzymes to the stress of PEF was investigated in this study. Unfolding of enzyme structures and disruption of secondary and three-dimensional structures occurred when the exposed PEF dosage exceeds a critical value, which caused the decrease in activity. In this work, sorbitol was found to be effective to stabilize the conformations and activities of enzymes against electric field. The protective effect increased with the increase of concentration of sorbitol.