In recent years there has been an increased awareness of the importance of those tissue changes which result from age. The numerous changes in the oral cavity of the rat include downgrowth of the epithelial attachment, increased inflammation, distal drift of the molars, loss of interproximal bone, continuous cemental deposition, and decreased width of the periodontal membrane.'-5 In a recent study on aging in mice,6 pocket formation, associated with accumulation of debris, was found to occur around the maxillary molars, but no downgrowth of the epithelial attachment was observed in the mandible. In the same study it was found that the non-trabecular bone of the 10-month-old animal became trabeculated and the marrow spaces filled with connective tissue by 24 months of age. Atrophy of the alveolar crest was not observed, although food impaction and inflammation increased with age. Studies on hamsters have disclosed an increased incidence of periodontal disease with increasing age.7-9 The disease process is characterized by accumulations of crevicular debris, inflammation, pocket formation, and downgrowth of the epithelial attachment. Using the smear technique in the study of the oral tissues of human patients, both increased keratinization10-12 and lack of change in the exfoliative cytology have been reported.'3 In another investigation on biopsied human gingiva, increased coarseness of the connective tissue fibers and decreased cellularity have been described.'4 No cytologic change was found in the epithelium or in the degree of cornification.'5 Atrophy of the prickle-cell layer of the oral mucous membrane, which can be modified by estradiol therapy, has been observed in postmenopausal patients.' In some aged individuals an atrophy of the oral mucous membrane, characterized by a loss of keratinization, loss of elasticity, and increased friability, has been described.'7' 18 In addition, a narrowing of the human periodontal membrane1 and a decrease in its cellular elements20 have been reported in the literature.In the present study, an attempt has been made to compare the aging patterns of two commonly used laboratory animals-the rat and the hamster-with those of a primate -the monkey. The studies on the rodents enabled us to observe the changes in lifespan in a short interval and compare them with those in a monkey. Presumably, the monkey may more closely simulate those changes which may be expected in the human.