Hemidesmosomal attachment of the junctional epithelial cells to the tooth and the ability of the attached cells to divide are essential features of the healthy dentogingival junction. Short chain fatty acids are bacterial metabolites associated with gingival inflammation and periodontal pockets. In vitro, short chain fatty acids have been shown to inhibit epithelial cell division and increase the density of their keratin filaments. This study examined these keratin changes by making use of human gingival keratinocyte cultures, gel electrophoresis and Western blot. Short chain fatty acids, butyrate and propionate, increased the relative amount of keratin proteins in the cells, most strikingly keratin K17. The distribution of K17 was further studied in a culture model for human junctional epithelium and in gingival biopsies. In butyrate-treated cultures of junctional epithelium, K17 expression was markedly increased and extended to the basal cells and to the cells mediating the attachment of the explant to the substratum. In clinically healthy gingiva, K17 was expressed predominantly in sulcular epithelium. The dividing basal cells and the cells attached to the tooth were negative. In advanced periodontitis, a strong reaction for K17 was localised to the pocket epithelium. The inhibition of epithelial cell division and the simultaneous upregulation of K17 in vitro, and the strong expression of this protein in detached pocket epithelium suggest a role for the short chain fatty acids in the degenerative process that leads to subgingival advancement of pathogens and, eventually, to periodontal pocket formation.