In clinically healthy/subclinically inflamed biopsies of marginal gingiva, the immunohistochemical distribution of keratin proteins was studied in junctional (JE), sulcular (SE), oral gingival (OGE) and in a few samples of alveolar mucosal epithelium (AE) by means of various mouse monoclonal anti-keratin antibodies in an indirect fluorescence technique. All regions stained in a nearly similar way with AE3 (keratins 1-8, all cells) and BE14 (keratin 5, basal and supra/parabasal cells). AE8-staining (keratin 13, supra/parabasal and spinous cells) was primarily confined to the stratified, nonkeratinized epithelia SE and AE, but also a variable part of JE and less frequently OGE were positive. The parakeratinized OGE was distinct in showing a homogeneous staining with AE2 (keratins 1/2, 10) and AE5 (keratin 3) throughout spinous cell layers. These antibodies did not stain JE and AE whereas SE stained in a scattered way with AE5 and sometimes also with AE2. The latter finding might indicate initial keratinization at molecular level. The JE was distinct in retaining basal characteristics throughout the epithelium with PKK2 (keratin 7, 16, 17, 19) and BE14 (keratin 5) although some initial suprabasal maturation, as observed with AE8, cannot be excluded. Differences in keratin staining of gingival epithelia and the AE was found with respect to AE1-reactivity (keratins 10, 14-16, 19) which was suprabasal in JE, SE and OGE but basal in AE.