Miniaturized glucose biosensors, prepared by electrochemical deposition of iridium and glucose oxidase (GOx), are characterized. The iridium network offers good retention of GOx and efficient preferential electrocatalytic detection of the liberated hydrogen peroxide at potentials lower than those of common interfering substances (the ascorbic acid signal actually shifts to a higher potential). The remarkable selectivity thus achieved towards the detection of glucose is coupled to a very fast response. Unlike analogous preparations of noble metal carbon fiber biosensors, a two-step electrodeposition process is required for the fabrication of Ir/GOx microelectrodes. The dependence of the biosensor response upon electrodeposition parameters, such as amounts of GOx and iridium or plating time is examined and optimized. Scanning electron microscopy is used to characterized the growth patterns of the iridium and Ir/GOx layers. The high selectivity associated with electrodeposited iridium matrices makes them very attractive for localizing other hydrogen-peroxide-liberating oxidases. oxidases. 1997 Elsevier Science S.A.