A sensor which responds very well to glucose in whole blood has been produced. Glucose oxidase is directly coupled to the platinum electrode by a silane coupling agent and is then cross‐linked with glutaraldehyde. This very thin catalytic layer is then covered with a rubber membrane. The response to glucose in whole blood is linear to at least 600 mg/dl with a small positive intercept. The response time is a few minutes. The key factor in the success of this sensor is the unitized construction in which the membrane and enzyme are chemibonded to the electrode. The compatibility with whole blood and high oxygen permeability of the membrane also contribute to the good performance.