Cyclic voltammetric responses are calculated for the reduction of a substrate at an electrode coated with a monolayer of catalyst with which the substrate must form a complex in order to be reduced. The effects of variations in the equilibrium constant for the formation of the catalyst-substrate complex, in the rate constant for its electroreduction and in the relative formal potentials of the catalyst and catalyst-substrate complex couples were evaluated. In every case the catalytic component of the total currents can be obtained by simple subtraction of the catalyst response measured in the absence of substrate. The peak potentials of the catalytic responses are usually more negative than the formal potential of the catalyst in the coatings. Both of these features differ from the behavior expected for the case where the substrate is reduced via outer-sphere electron-transfer to the catalyst coating [3]. The situations in which the voltammetric responses may be used to discriminate between these two mechanisms are discussed.