Electrode systems are disclosed for measuring the concentration of an analyte under in-vivo conditions, where such systems include a counter electrode having an electrical conductor, a working electrode having an electrical conductor on which an enzyme layer containing immobilized enzyme molecules for catalytic conversion of the analyte is arranged, and a diffusion barrier that slows the diffusion of the analyte from body fluid surrounding the electrode system to enzyme molecules. The enzyme layer is in the form of multiple fields that are arranged on the conductor of the working electrode at a distance from each other.
