Electrochemical and catalytic properties of vitamin Bit hexacarboxylate-polylysine films covalently immobilized onto pyrolytic graphite electrodes were controlled by microemulsion composition. Sodium dodecyl sulfate (SDS) in microemulsions and micellar solutions is incorporated to form micelles within the cationic films. This changes the net film charge from positive, characteristic of the protonated lysines, to negative, characteristic of SDS micelles. Micelle formation was supported by voltammetry and quartz crystal microbalance results, which also suggested that cationic surfactants do not enter the film. Catalytic turnover rates for the reduction of dibromocyclohexane to cyclohexene mediated by the film in SDS microemulsions were controlled by the difference between the reduction potential of the reactant and the catalyst E-o' in the film. Thus, reaction rate in these systems is controlled by the intrinsic activation free energy. For a given reactant, catalyst E-o', and consequently activation free energy, can be controlled by microemulsion composition via interactions of surfactant and salt with the polymer network. Fast catalyst turnover was also facilitated by high conductivity and low viscosity of the bulk microemulsion.