In a previous communication (Langmuir 1997, 13, 6980-6984) we reported stabilization of water-in-CO2 (wic) microemulsions by fluorinated dichained sulfosuccinate surfactant ＇di-HCF4＇. In this paper we present a study of enzyme-catalyzed reactions affected in this w/c microemulsion in which the enzyme is located within the dispersed water droplets. Two reactions, a lipase-catalyzed hydrolysis of p-nitrophenol butyrate and lipoxygenase-catalyzed peroxidation of linoleic acid were examined. The activity of both the enzymes in the w/c microemulsion environment were essentially equivalent to that in a water-in-heptane microemulsion stabilized by Aerosol OT, a surfactant with the same headgroup as di-HCF4. The inherent condition of low pH of the water droplets in the w/c microemulsion was improved using the buffer MES [2-(N-morpholino)ethanesulfonic acid] which was shown to fix the pH in the range 5-6 depending on buffer concentration, pressure, and temperature.