To overcome the problem of metabolic crashes as hypoglycaemic as well as hyperglycaemic episodes in diabetic patients the continuous or at least very frequent checking of the circulating intracorporal glucose concentration is necessary. Biosensors measuring glucose in vivo are suitable for estimating the transient interstitial glucose concentration in human beings. Biologically and/or biochemically caused processes are responsible for limiting the functional stability of implanted sensors. It is now possible to advance beyond the current practice of hand making glucose sensors in the laboratory and produce these sensors as industrial products with reproducible characteristics. This gives us a real chance to avoid hypoglycaemic and hyperglycaemic metabolic attacks.