Glucose oxidase, catalase, and bovine serum albumin were co‐immobilized with glutaraldehyde around a platinum screen or around a single platinum—iridium wire. The potential difference between this dual enzyme electrode and a Ag/AgCl reference electrode was proportional to the logarithm of the glucose concentration over the range from 10 to about 150 mg glucose per 100 ml in buffered solution at pH 7.4 and 37°C. The enzyme electrode responded in serum only if coated with a semipermeable film, such as cellulose acetate, to exclude serum macromolecules. The potentiometric results were similar to those obtained with the two enzymes co‐immobilized in polyacrylamide gel around a platinum screen or with only one of the enzymes, glucose oxidase, covalently coupled to a platinum screen. The results so far suggest that these potentiometric enzyme electrodes may have sufficient specificity for glucose for development of a continuous in vivo glucose sensor.