‘ ronment highly contaminated with radioactive material. The radioisotopes of strontium, barium and iodine, along with some of the rare earths, were absorbed in greatest amount. Probably, only isotopes of iudine exceeded the accepted permissible levels. No acute effects of exposure from the internally absorbed radionuclides were observed. Since their return to Rongelap in 1957 the people have been exposed to low levels of certain residual radionuclides — namely, Cs", Zn® (this is an induced radioelement) and Sr, Body burdens appear to have reached equilibrium with the environmental levels of these elements, and are well below the accepted permissible range. LATER FINDINGS Evaluation of the general health status, illnesses, mortality, fertility and aging over the eleven years since exposure has revealed no significant differences between the exposed and the unexposed pop- ulations that could be attributed directly to radia- tion. The slight lag in recovery of peripheral blood elements has not affected their resistance to disease and immunologic competence. Although the birth rate has been about the same in the exposed and unexposed groups there was an apparent increase in miscarriages and stillbirths in the exposed women as compared with the unexposed women over the four vears after exposure (41 per cent, or 13 of 32 pregnancies in the exposed, as compared with 16 per cent, or 8 of 49 pregnancies in the unexposed womenover a comparable period). A few congenital abnormalities have been observed in babies born to exposed women, but no correlation with radiation seems possible at present. Slit-lamp observations have failed to reveal radiation-induced opacities of the lens. Studies of growth and development? comparing 42 exposed with 75 unexposed children have revealed a slight retardation of growth in the boys exposed at one to five vears of age, most marked in those exposed at twelve and eighteen months of age. The possibility that radiation was a causative factor will be discussed later. CONSIDERATION OF THE RADIATION DOSE TO THE THYROID GLAND Calculation of the dose to the thyroid gland from radioactive iodine requires knowledge of its uptake by the gland, its half-life in the gland, the size of the gland and the relative proportion of the several radioisotopes of iodine. Unfortunately, in the present situation few data of a direct nature are available. The relative’ distribution of radioiodines in fallout is well known. In addition to I", the isotopes of 1'3, P55 and to a lesser extent I? contributed significantly to the thyroid dose. The only data available are radiochemical analyses of pooled urine samples taken fifteen days and longer after the fallout. Three separate estimates of the dose to the thyroid glands of adult Rongelap people from radioiodines have been made: 150 rads (from direct measurements of urinary I'8'}; 100 rads (by indirect measurements using animals — pigs removed from Rongelap — and Marshallese urinary-excretion data)®; and 160 rads (based on recent recalculations of early data).6 The last recalculations® were based on analysis of pooled urine samples mainly from adult Rongelap people taken fifteen days after detonation; an estimate of the one-day thyroid content of I'3} was 11.2 microcuries (5.6 to 22.4 microcuries) assuming that 0.1 per cent (0.05 to 0.2 per cent) of the maximum thyroid burden was excreted in the urine on the fifteenth day. The dose of 160 rads to the adult thyroid gland was calculated from oral intake and inhalation of the various iodine isotopes, considering their fission yield, the average energy deposited in the thyroid gland per disintegration and the time of absorption. The dose to the thyroid glands of children three to four vears old was then calculated by means of these factors with consideration of pulmonary function and the thyroid size? of a child that age. Water was regarded as the main source of iodine ingestion, and since water was being rationed at the time of the fallout, it was assumed that the children drank the same amount of water as adults and theretore had the same thyroid burden of radio- iodines. Because of the small size of the gland the beta dose of radiation to the gland was substantially larger. The total estimated dose from the various iodine iso- topes to the child’s gland was about 1000 rads, with a minimum of about 700 rads and a maximum of 1400 rads. The glands received an additional 175 rads from external gammaradiation. Details of these calculations have been given by James and Gofman® Though the skin overlying the thyroid gland was frequently the site of “beta burns” it is not believed that the deposits of radioactive materials in this area added significantly to the thyroid dose since most of the beta irradiations were of insufficient energies to have penetrated to the depth of the gland. ABNORMALITIES OF THE THYROID GLAND Physical examinations have always included careful inspection of the thyroid region in both exposed and unexposed comparison groups. In addition, determinations of the level of protein-bound iodine and cholesterol in serum have been carried out at various intervals since 1959 in some persons. Until 1963 no thyroid abnormality was detected in either the exposed or the comparison population, except for 1 case of asymptomatic diffuse thyroid enlargement seen in an unexposed woman. The average level of serum protein-bound iodine was found to be elevated in both the exposed and comparison populations. It is believed that this is a racial characteristic, and that the increase is partly due to an increased level of the iodoprotein fraction of serum.* No significant differences were noted between the mean. protein-bound iodine and cholesterol levels in