The goal is the development of an electrochemical glucose sensor which is capable of being implanted into the vascular or extracellular space of a diabetic patient for continuous in vivo monitoring of his blood sugar level. Its use would eliminate the inconvenience of intermittent withdrawal of blood for glucose assay, as well as the control lag which this imposes. A direct bedside readout would benefit the acute case of diabetes and such a sensor, when coupled with an insulin infusion pump, and interfaced with a feedback system, would complete the development of an integrated artificial endocrine pancreas. A number of pumps and feedback systems are currently under clinical evaluation in the United States. Central to the artificial pancreas is the glucose sensor which is far behind the other components in its development. The availability of such a sensor would constitute a breakthrough for both clinical practice and basic investigation of diabetes and its associated complications. Potentiodynamic studies have revealed two new distinct low-potential redox peaks at the smooth Pt electrode that can be utilized for glucose monitoring even in the ultrafiltrate of human serum. This reaction is reproducible since the electrode surface is regenerated by electrochemical pulsing. The two peaks are located at well-defined potentials: -0.72 V (anodic oxidation) and -0.80 V (cathodic reduction) vs Ag/AgCl. These potentials are stable and do not shift with increasing glucose concentration. The in vitro study has shown that an electrode using this reaction should be operable at glucose levels up to 400 mg/dl. The specific aims are: (1) to construct a standard, controlled geometry test electrode using thick film deposition technique; (20 to use this electrode in parametric tests to characterize the mechanism by which the redox peaks are generated; (3) to select the proper voltammetric conditions for the practical development of the sensor; (4) to evaluate the specificity of the peaks for glucose in the presence of potentially interfering substances which might be present in human blood and tissue fluid; (5) to determine if trace amounts of Pat and Ag are released during prolonged voltammetry; (6) to design and construct a miniaturized, implantable electrode array using thin film deposition techniques.