The present study includes a reexamination of 10 patients who, two years ago received complete upper and lower denture treatment to eliminate an existing denture stomatitis. Clinical healing of the denture stomatitis was obtained only in one patient, whereas the remaining nine patients still displayed an obvious denture stomatitis. Biopsies were taken from the palatal mucosa and examined histologically, microradiographically, and by electron microscopy. The results of these examination indicated that, in denture stomatitis there is a reduced thickness of the epithelium, an absence of a stratum corneum, a markedly widened intercellular space, especially in the stratum basale, and an intense infiltration of inflammatory cells, plasma cells and lymphocytes in the connective tissue, as well as in the epithelium. These changes are characteristic features of an inflammatory process, and similar to the changes which occur, for example, in chronic, marginal gingivitis. The composition of the inffammatory infiltrate suggested that, in denture stomatitis, immunological phenomena influence the pattern of the tissue reaction.