6 days whenthe bodylevels were at their highest, the maximum permissible concentrations were approachedorslightly exceeded only in the case of strontium-89 andtheisotopesof iodine. At that time the concentrations were believed to be too low to result in any serious effects. Body levelsfell rapidly, so that by 2 and 3 years post exposure they were far below the accepted maximum per- missible level; even by 6 months activity in the urine wasbarely detectable. In 1958 analyses of bone samples on oneofthe men whodied showed a body burden of 3.7 nCi Sr. Beginning in 1957, gammaspectroscopy by use of a low-level counting chamber was added to the techniques of radiochemical analysis. The return of the Rongelapese to their homeisland (which after careful survey was considered safe for habitation, despite a persisting low level of radio- active contamination) wasreflected in a rise in their body burdens and increased urinary excretion of certain radionuclides. During the 4 years after the original contaminating event, additional weaponstests held in the area contributedslightly to the fission products in the environment. S -ce the diet includes a variety of imported foods. .ne people may have been delayed in reaching equi- librium with the environmentalfission products. Body burdens of gamma-emitting fission products (such as '*’Cs and **Zn) were measured ina whole-body counter and checked by radiochemi- cal analysis of urine specimens. Thelevels ofinternal contamination per unit weight appeared to be about the samefor juveniles as for adults, male body burden was 0.67 uCi, whichis slightly higher than the mean valueof a similar group obtained in 1959; it was 300 times that of the medical team, who were measured at the sametime for compari- son. It appearedatthis time that the peopte were approaching equilibrium with their environment. The ©Zn level dropped to 0.071 wCi in 1959. With a larger detector and a longer counting time than previously employed, it was possible to identify and quantify °°Cofor thefirst time in these people; the mean level of °°Co was about 11% of the Zn level (7.6 nCi). A small amountof residual activity wasstill present after the subtraction of *°K and the above radionuclides from the total spectrum. The mean level-of urinary excretion of °°Sr was 7.2 pCi/i or 14%higher than measured in the 1959 medical survey:-in 1962 the mean urinary, *°Sr level was 114 pCi/g Ca, givigg-gm estimated. body burden of 12.0 nCi. Analysis ofbones fom the deceased Rongelap woman (1962) gave an estimated body burdenof 11.4nCj. Theselevels represent about a.6-fold intreasejin *“Sr over the 1958 levels. The levels of °°Sr in 1962 and 1963 hovered around the 12.0-nCi level in adults and about 22 nCi in children, about 5 and 10% respec- tively of the maximum permissible level (for members of the populationatlarge). It thus appears that body burdensof °°Sr have reached equilibrium with the environmental °’Sr. Little or none of the present body burden of the exposed group can be considered residual from their initial exposure, since little difference has been noted between the body burdensin exposed and female. Widevariationsin levels of contamination were found, apparently due to differences and unexposed populations living on Rongelap in diet, metabolism, and age. tion of radioiodinesinitially in the fallout to the Body burdensof °°Sr were estimated from urinary excretion as determined by radiochemical analyses. Both the external dose measurements on Rongelap Island andthelevels of radioactive isotopes in the food on the Island indicated that some increase in '*’Cs, ®°Zn, and *°Sr body burdens was to be expected when the people returned there in 1957. The '*"Cs body burden in 1958 was about 0.68 uCi, about 60 times as great as in 1957, and the urinary **’Cs level rose by a factor of 140; the mean body burden for 1959 was 0.57 pCi. The mean body burden of *°Zn estimated from whole- body counting data was, in 1958, after the return to Rongelap, 0.36 uCi, 8 times as high as in 1957, and 0.44 pCi in 1959. In 1961 the mean '*7Cs Island. The possible relation of internal absorp- recent developmentof thyroid nodules will be referred to later. No other effects of such exposure have been detected. OTHER STUDIES Studies of Genetically Inherited Characteristics: Blood grouping studies in the Marshallese showeda relatively high B gene frequency, a high N genefrequency, an extremely high R' gene frequency, and total absence of Kell and Diego factors.'* These characteristics differ from those of Polynesians and suggest relationship with Southeast Asians and Indonesians. Haptoglobin studies showed the frequency of the Hp' geneto be higher than in Euro-