The changes of barrier properties and surface cytology of the palatal mucosa during a denture-wearing period of 12 months has been studied in 18 adult subjects. Transmucosal rates of water transport and that of a 1.10 osmol sucrose solution were registered gravimetrically before denture treatment, after 3 months and after 12 months of denture wearing according to procedures described earlier. The keratinization pattern and the leukocyte migration were evaluated from scrapings taken from the palate and the fitting surface of the denture. The clinical appearance was recorded photographically. After 3 months of denture wearing only minor changes in permeability and surface cytology were observed. After 12 months a distinct grouping of the material was possible with regard to permeability reactions, as seven subjects showed no changes, five subjects demonstrated an increased osmotic activity in the palatal mucosa, and six subjects exhibited a severely decreased barrier function. The color photos revealed inflammatory reactions of the palatal mucosa in the latter group. The cytologic observations showed after 12 months a significant decrease in the proportion of anucleated cells in the inflammatory group, but only minor changes in the remaining material.