Specimens of human gingiva were collected from teenage and adult subjects and frozen sections were stained with an extensive panel of monoclonal antibodies with defined specificities for individual cytokeratins. The results indicated different and distinctive patterns of keratin expression by the oral gingival, oral sulcular and the junctional epithelia. It was observed that epithelium with staining characteristics of sulcular epithelium extended over the gingival crest onto the oral surface of the gingiva. Junctional epithelium showed the unusual pattern of co-expression of keratins typical of the stratifying and of the simple epithelial phenotypes. The patterns of gingival keratin expression are compared with those of other mucosal epithelia. The findings are discussed in relation to mechanisms that may determine or influence the junctional epithelial phenotype.