We have modeled the steady state current generated at a microdisk enzyme electrode where a reaction product of the enzyme reacts at the electrode itself. Simple approximate expressions have been derived for the response in limiting cases, as well as a semiempirical expression suitable for all cases. The model was tested using Pt microdisks modified by films of poly(vinyl alcohol) containing glucose oxidase. From the variation of the current with film thickness, the diffusion coefficient of glucose in the film was estimated, as well as the value of k(cat)/K-M for the immobilized enzyme. (C) 2003 Elsevier B.V. All rights reserved.