A kinetic model is presented for the electroenzymatic processes occurring at a polyphenol oxidase rotating-disk-bioelectrode for low concentrations of catechol. The work presented here is based on the same formalism as that previously used by Bartlett and Whitaker (J. Electroanal. Chem., 224 (1987) 27) for a glucose sensor. Our model allows one to analyze the effect of enzyme loading, film thickness, permeability and electrode rotation rate. It also unambiguously demonstrates for the first time that the high sensitivity and low detection limit observed for such an enzymatic electrode is the consequence of the electrochemical recycling of substrate which occurs upon transduction.