A membrane-covered oxygen electrode coated externally with a noble metal catalyst black can be used for rapid continuous measurement of dissolved reducing sugar. The catalyst promotes the reaction between the sugar and dissolved oxygen to form sugar oxidation products (e.g. gluconic acid) and water. Accordingly, the diffusive flow of unreacted oxygen into the electrode is related inversely to reducing sugar concentration. Body fluids (e.g. plasma, urine) tend with time to diminish catalyst activity. The catalyst has been regenerated electrochemically in situ by brief application of negative potential pulses. Improvements in the design of the catalyst matrix may make it possible to accomplish this regeneration repeated in vivo. With further development, such a catalystcoated electrode may be the sensor for a self-contained totally implantable artificial organ that would continuously monitor sugar concentration in a body fluid of a diabetic and meter out insulin in proportion to need.