The invention relates to an electrode system for measuring the concentration of an analyte under in-vivo conditions, comprising a counter-electrode (2) having an electrical conductor (2a), a working electrode (1) having an electrical conductor (1a) on which an enzyme layer (5) 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 down.The invention provides the enzyme layer (5) in the form of multiple fields that are arranged on the conductor (1a) of the working electrode (1) at a distance from each other.本發明有關一種用於在活體內條件下測量分析物濃度之電極系統,其包含具有導電體(2a)之相對電極(2);具有導電體(1a)之工作電極(1),該導電體(1a)上配置有含有用於催化轉化該分析物之經固定化酶分子的酶層(5);及減緩該分析物自環繞該電極系統的體液擴散至酶分子的擴散障壁。本發明提供在該工作電極(1)之導電體(1a)上以彼此相距某距離而配置的多域(multiple fields)形式之酶層(5)。