A glucose biosensor, based on glucose oxidase immobilized in a non-conducting (overoxidised) polypyrrole film, is described which proved practically immune from faradaic interference arising from endogeneous (ascorbate, urate, cysteine) and exogeneous (acetaminophen) electroactive interferents. The bias introduced in the measurement of 5 mM glucose by the given interferents at their maximum physiological levels never exceeded 2% which is, by far, the lowest value ever reported. The biosensor has been used for continuous subcutaneous monitoring of glucose in a rabbit implanted with a microdialysis probe. The potential and limits of this approach are discussed.