We have developed a miniature glucose sensor using an oxygen electrode with a glucose oxidase membrane. The special character of this sensor is that the electrodes can be placed in a blood vessel and can measure the glucose level directly from the arterial blood stream if placed into an external A-V shunt. Its second notable characteristic is that the enzyme membrane is covered with a semipermeable membrane, which partially allows passage of glucose but only sufficient oxygen. This sensor is able to respond to glucose concentrations of up to 700 mg/dl in blood. This sensor loses 10% of its activity at about 200 h of continuous use, and 30% after 400 h of use. While the sensor cannot be sterilized by conventional mechanical or gas methods, certain antibiotics can be used for sterilization. To shorten the response delay of the sensor during the decreasing phase of glucose concentration, a thinner membrane is under development.