Abstract We have constructed and tested in vitro a potentially implantable, needle-type amperometric enzyme electrode which is suitable for continuous monitoring of glucose concentrations in diabetic patients. The major requirements of stability during operation and ease of manufacture have been met with a sensor design which involves a simple dip-coating procedure for applying to a platinum base electrode an inner membrane of glucose oxidase immobilised in polyhydroxyethyl methacrylate (pHEMA), and an outer membrane composed of a pHEMA/polyurethane mixture. Sensors were operated at 700 mV for detection of hydrogen peroxide. Calibration curves for the sensor were linear to at least 20 m m glucose and were unaffected by a reduction in P O 2 from 20 to 5 kPa. During continuous operation in 5 m m buffered glucose solutions in vitro, sensors suffered no significant loss of response over periods of up to 60 h. Such electrodes are, therefore, useful for development as in vivo glucose sensors.