In enzyme catalysis there is great interest in finding suitable organic media for less water-soluble substrates in order to increase the substrate concentration and, therefore, the reaction rates. These requirements are fulfilled by using microemulsions as reaction media. In this study w/o-microemulsions were used to investigate the kinetics of the reduction of 2-Heptanone to S-2-Heptanol, catalyzed by alcohol dehydrogenase. The required cofactor NADH for this reduction is regenerated by a second enzyme, formate dehydrogenase. The influences of pH, temperature, and the kinetic parameters of the enzymes are presented. It is demonstrated that in microemulsions the reaction rate of ADH is increased up to 12 times compared to water.