A previous study demonstrated structural differences in the junctional epithelium between juvenile and adult dogs. In juveniles the junctional epithelium showed some resemblances to the oral gingival epithelium, and a cuticular structure at the dento-gingival junction was of particular interest. The oral gingival epithelium is considered to be less permeable than the junctional epithelium. As cytoplasmic filaments are held to be the main component in the process of keratinization, and to have a stabilizing influence on the cells and tissues, the present investigation was designed to study the relative amounts of cytoplasmic filaments in the junctional and the oral epithelia of beagle dogs during juvenile and adult stages. In addition, the ultrastructure of the dento-gingival junction was characterized. Six beagle dogs were used. The material consisted of gingival biopsies sampled when the dogs were 3 and 12 months old, respectively. On these occasions the gingiva was in excellent health. The biopsies were prepared for electron microscopic analysis and three randomly selected fields were recorded photographically from each of the following epithelial strata: basal and granular cell layers of the oral epithelium and basal and superficial cell layers of the junctional epithelium. Morphometric analysis was performed in order to estimate the density of cytoplasmic filaments of the cells in these epithelial strata. The amount of cytoplasmic filaments was considerably lower in the cells of the junctional epithelium than in those of the oral epithelium. In the oral epithelium the amount increased from basal towards superficial cells, whereas no such increase was seen in the junctional epithelium. The pattern was the same in the juvenile and the adult stage. At the dento-gingival junction all dogs had a thick, laminated layer of dental cuticle material in the juvenile stage. In the adult stage a similar structure was seen only infrequently, and it never attained the thickness observed in the juvenile stage.