Effects of multiple sublethal doses (6 weekly exposures of 200 r each) on the subsequent appearance of the periodontal and dental tissues were studied in male mice fed either a highly purified diet complete in all know nutrients or a natural food stock ration. Periodontal lesions were observed in x-irradiated animals on the purified diet 100 days following the 1st irradiation exposure, but not prior to this time. The subsequent development of the lesions generally paralleled that of primate periodontitis and was characterized by plaque formation, gingival recession, periodontal destruction, dental necrosis, and exfoliation. In contrast, no periodontal pathology was observed in xirradiated mice on the stock diet. Multiple sublethal x irradiation appears to be a primary etiologic factor in the formation of periodontal lesions in mice fed the purified diet. Secondary factors, such as age, diet, trauma, oral bacterial flora, heredity, may also be implicated. Two manifestations of radiation injury, namely, diminution of body resistance to infection and the so-called aging effect of radiation, should be considered too. Histologic studies indicated that salivary function, particularly of the palatal gland system, was impaired. Areas of fibrosis and reduced glandular tissue were prominent in several irradiated animals on the purified diet.more » This suggests a more specific type of radiation- induced somatic lesion, with its focus upon the oral environment. Impaired salivary function could play an important etiological role in the lesions observed, by facilitating the accumulation of plaque material. (H.H.D.)« less