Abstract: A device for the continuous quantitative determination of glucose in the blood of a diabetic patient over a period of 24-36 hours, comprises a container for a saline solution with heparin, a microdialyzing needle inserted into a vein of a diabetic patient, a pump for injecting the solution into the microdialyzing needle, a semipermeable hollow fiber membrane located externally of the needle whereby dialysis occurs between the blood and the solution and only glucose and other substances of low molecular weight below 100,000 daltons go through the membrane and the concentration of the glucose and other substances of low molecular weight below 100,000 daltons inside the needle is proportional to that of the external side of the membrane. The needle is provided with an outgoing conduit, the conduit leads to a sensor, which comprises an enzymatic membrane coupled with a Platinum-Silver electrode.