The intraoral clinical findings obtained in March 1959 on Marshallese natives 5 yr after exposure to total-body irradiation from sudden, significant quantities of radioactive fallout are described. This fallout was precipitated on Rongerik atoll, Rongelap atoll, Ailingnae, and Uterik in the Marshall Islands after detonation of a 15-Mt thermonuclear test device at the Bikini Proving Grounds in February 1954. As a result, 239 Marshallese were accidentally exposed to total-body irradiation ranging from 14 to 175 r. Examinations disclosed similar degrees of caries activity in irradiated and nonirradiated children. Although the prevalence of periodontal disease was practically identical in both the irradiated and nonirradiated groups, the extent of periodontal destruction was greater in the irradiated Rongelapese. This difference may or may not be related to factors such as leukopenia and lower tissue resistance and the presence of preexisting periodontal disease. Children born of irradiated parents, including those children in utero at the time of initial exposure, and irradiated children 6 to 18 yr old, showed no evidence of any morphologic effects on oral tissues from total-body irradiation when compared with the nonirradiated control groups. No evidence of intraoral neoplasm was noted; however, one 42-yr- old irradiated Rongelap man had a smallmore » leukoplakic-like lesion on the gingiva. No clear relation of radintion exposure in the Rongelap people to the higher levels of periodontal destruction in this group is suggested. Because of the generally substandard levels of oral hygiene among the Marshallese, it is likely that the disease was prevalent at the time of their radiation exposure. However, the period of leukopenia after this group's exposure might have enhanced the progress of periodontal disease, although they showed no evidence of increased infection, oral or otherwise, or bleeding tendency during the period of leukopenia and thrombocytopenia. (BBB)« less