Pressurization of enzyme-containing AOT-water-isooctane reversed micelles with low molecular weight gases leads to markedly different responses in activity characteristics. Microbial lipases exhibit a total cutoff in activity with as low a pressure as 2 Wa and a remarkable activity regain with depressurization. The observation also holds for reaction in monophasic organic solvents. The protease, alpha-chymotrypsin, is unaffected by pressurization until a critical pressure wherein micellar instability occurs. The use of pressure as a switch for lipase reaction in nonaqueous media is discussed.