Medical teams almost always included an equal complement of Micronesians trained as medical practitioners, nurses, health aides, and technologists. These participants were especially valuable in obtaining accurate interval histories, which were primarily directed toward detecting conditions with higher probabilities of radiation association, such as thyroid enlargement or dysfunction or development of neoplasia in other organ system. * Family and social histories were also obtained to establish pedigrees, periods of residence on various islands, and smoking and drinking habits, and to supplement demographic data obtained by other means. Thorough general physical examinations were administered by the medical staff with special attention directed to examination of the thyroid, skin, female breasts, and other sites of potential oncogenesis. Preprinted examination protocol forms ensured uniformity and completeness. Questionable find- ings were evaluated by consultation with other staff physicians. Positive thyroid findings were always confirmed by a consulting thyroidologist before more extended evaluations and/or surgery were performed in the United States (see Section IX.B). Patients 40 years of age or older received standard 12-lead electrocardiograms annually (Hewlitt-Packard 1500), a 14x17-inch P-A chest x ray biannually (or more frequently if indicated by smoking history and/or signs or symptoms of pulmonary pathology), and annual stool examinations for occult blood (Ames Hemocult). Urine was tested for pH, sugar, acetone, blood, and protein with Ames Labstiks. Blood for hematologic and endocrine evaluations was drawn and processed as described in Section III.B. Two-hour postprandial blood sugars were measured annually in known diabetics and periodically in the entire study group, and glucose tolerance tests were periodically administered (see Section VII). Other biochemical assays, such as those for serum enzyme activity and electrolyte and metabolite concentrations, were performed at irregular intervals or as clinically indicated in certain individuals. Dental examinations have been limited essentially to extractions and fluoride prophylaxis. Periodic ophthalmologic examinations have included slit-lamp inspection for cataracts but not refractions (1). The pediatric study groups consisted of all children exposed to radiation in March 1954 and a comparison population selected from unexposed Rongelap children in 1957 who were matched as closely as possible for age and sex. Attrition in the control group due to death or emigration was compensated by periodic addition of unexposed individuals. Children born to parents in the adult study groups were also examined routinely as a separate study group. The initial composition of these groups is summarized in Table 2. Rongelap children in each group were examined, generally on an annual basis, by the medical team, which included a pediatrician each year since 1958, ex-cept for the four years 1960, 1964, 1967, and 1973. In earlier years, the children on Utirik were not seen as frequently as those on Rongelap, but major efforts to examine them were mounted in 1957, 1959, 1966, 1969, 1972, and each year since 1974, when examinations were performed at least annually on all study groups whether they were residing at Rongelap, Utirik, Majuro, or Ebeye.