The substantiation of periodontal changes and the evacuation of their course must always involve exact measurements. Up to now the thickness of the gingiva and its dimensional changes have been neglected in most studies though such data may be very revealing in assessing the tissue. The author designed a device which permits to measure the recession of the gingiva with an accuracy of 1/10 mm and to determine exactly the thickness of the gingiva. The thickness of the gingiva was measured in a group of patients undergoing an oral irrigation cure. An initial soft-tissue reaction (in which the opening of terminal vessels and swelling processes seems to prevail over the flooding-out of oedemas) is followed by a small reduction in gingival thickness (presumably associated with the flooding-out of oedemas). The results so far obtained correspond to the clinical, stomatoscopical and bioptical observations.