We adapted a new technology for the modification of carbon base electrodes for use as probe-type, potentially-implantable glucose sensors. Carbon rods (diameter 0 3 mm) were modified by repeated potential cycling in 0 1 M potassium hexacyanoferrate (III). The modified-carbon electrodes were sealed in plastic pipette tips with an exposed reaction area where glucose oxidase was immobilized using glutaraldehyde. An outer membrane of Nafion, followed by 15% (w/v) polyurethane, was applied over the enzyme layer. The miniature modified-carbon glucose sensors displayed a sensitivity to glucose in phosphate-buffered saline of 91 4±19 nA/mM (mean±SEM) and a linear range up to 5 3± mM glucose when operated at 750 mV versus a silver/silver chloride reference. Corresponding, unmodified-carbon based glucose sensors displayed a lower sensitivity of 20 7±3 nA/mM with a linear range up to 3 8±0 5 mM. The modified-carbon glucose sensors responded to glucose when operated in plasma but with a reduced sensitivity compared with that in buffered saline. Glucose sensors displayed good stability for up to 6 5 days during continuous operation in 5 mM buffered glucose solution. Interference from ascorbate and 4-acetamidophenol at both physiological and pharmacological ranges was significantly lower at the modified-carbon base electrodes than that at the unmodified-carbon base electrodes. Also, the relatively large effect of ascorbate and 4-acetamidophenol at the unmodified-carbon base electrode was reduced considerably when the base electrode was coated with glucose oxidase, Nafion and polyurethane membranes.