Abstract: A method for determining and monitoring tissue glucose concentration, wherein a perfusion solution is conveyed as a liquid column through a microdialysis probe implanted in the tissue and is moved to a test cell preferably arranged outside the patient's body, the volumetric flow of the perfusion solution being reduced in its time average for the duration of the dialysis intervals (T.sub.1) and the volume of the perfusion solution perfused through the microdialysis probe during each dialysis interval (T.sub.1) being moved on in a consecutive transport interval (T.sub.2) at a higher volumetric flow to the test cell and wherein the glucose content of the perfusion solution passing through the test cell is determined from continuously detected test signals, characterized in that before passing through the microdialysis probe the perfusion solution is mixed with glucose in order to set a predetermined initial concentration.