Constant current voltametry was shown to be a suitable method for evaluation of electrodes containing immobilized oxidative enzymes as catalysts. The half‐cell potential for the oxdidation of D‐glucose at constant pH was measured at a series of constant dc currents, using glucose oxidase immobilized in a polyacrylamide gel‐platinum gauze matrix as catalyst. Over the range studied the potential versus current data were linear and could be extrapolated to give the open‐circuit half‐cell potential at zero current. The difference between the measured potential and the open‐circuit potential at a constant current was indicative of the loss in useful voltage due to concentration gradients within or adjacent to the enzyme electrode assembly. The relationship between the open‐circuit potential and the pH of the reaction mixture was linear with a slope of −0.056, in good agreement with the predicted slope of −0.061.