Abstract: An electrode cell assembly for the continuous determination of ion concentrations in living tissues, which cell assembly comprises a measuring electrode having an ion selective member, which is shaped in a way so that it can be introduced into the living tissue and which cell assembly, furthermore, has a reference electrode in a housing which is filled with an electrolyte and which housing of the reference electrode has a membrane which is in continuous contact with the surface, e.g., the skin or the tissue of the living being during the determination of the ion concentrations, so that the ion concentration can be continuously read off from a recording device with which the electrode cell assembly is connected.