6 days when the bodylevels were at their highest, the maximum permissible concentrations were approachedorslightly exceeded only in the case of strontium-89 and the isotopes of 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 mon..s activity in the urine wasbarely detectable. : 1958 analyses of bone samples on oneof the men whodied showed a body burden of 3.7 nCi Sr. Beginning in 1957, gammaspectroscopy by body burden was0.67 Ci, whichis slightly higher than the mean valueof a similar group obtained in 1959; it was 300 times that of the medical team, whowere measured at the same time for comparison. It appearedatthis time that the people 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 the first time in these people; the meanlevel of *°Co was about 11% of the ’*Zn level (7.6 nCi). A small amountof residual! activity 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- 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/! or 14% higher than measured in the 1959 medicai survey. In 1962 the mean urinary “°Sr level was 114 pCi/g Ca, giving an estimated their body burdensandincreased urinary excretion of certain radionuclides. During the 4 years after the original contaminating event, additional estimated body burden of 1:4 nCi,.These levels represent about a 6-foldingrease irr Sr over the to the fission products in the environment. Since the diet includes a variety of imported foods, the people may have been delayed in reaching equilibrium with the environmental fission products. Body burdens of gamma-emittingfission prod- bers of the population atlarge). It thus appears that body burdensof °°Sr have use of a low-level counting chamber was added to active contamination) was reflected in a rise in weaponstests held in the area contributed slightly ucts (such as '°'Cs and °°Zn) were measured in a whole-body counter and checked by radiochemi- cal analysis of urine specimens. Thelevels of internal contamination per unit weight appeared to be about the samefor juveniles as for adults, male and female. Wide variationsin levels of contamination were found, apparently due to differences in diet, metabolism, and age. Body burdensof *°Sr were estimated from urinary excretion as determined by radiochemical analyses. Both the external dose measurements on Rongelap Island andthe levels 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 timesas 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 burdenof *°Zn estimated from wholebody counting data was, in 1958, after the return to Rongelap, 0.36 uCi, 8 times as high as in 1957, and 0.44 uwCi in 1959. In 1961 the mean '°’Cs body burden of 12.0 nCi. Analysis e€ bones from the deceased Rongelap wagiimn (1962) gave an 1958 levels. Thelevels of *Sr in 1962 and 1963 hovered around the 12.0-nCi level in adults and about 22 nCiin children, about 5 and 10% respectively of the maximum permissible level (for mem- reached equilibrium with the environmental *’Sr. Little or none of the present body burden ofthe exposed group can be considered residual from their initial exposure, since little difference has been noted between the body burdensin exposed and unexposed populations living on Rongelap Island. The possible relation of internal absorption of radioiodinesinitially in the fallout to the 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 frequencyof the Hp’ geneto be higher than in Euro-