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 isotopesof iodine. At that time the concentrations were believed to be too low to result in any serious effects. Body levels fell rapidly, so that by 2 and 3 years post exposure they were far below the accepted maximum permissible level; even by 6 monthsactivity in the urine was barely detectable. -body burdei was 0:67 pCi, which isslightly higher than the mean value of a similar groupobtained in 1959; it was 300 times that 6Pthe medieal team, who weremeasuredat the same time for comparison. It appeared at this timethat the people were men who died 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 home island (which after careful survey was considered safe for habitation, despite a persisting low level of radio- level (7.6 nCi). A small amountof residual activity In 1958 analyses of bone samples on one of the active contamination) was reflected in a rise in their body burdensand increased urinary excretion of certain radionuclides. During the 4 years after the original contaminating event, additional weapons tests held in the area contributedslightly to the fission products in the environment. Since the diet includes a variety of imported foods, the people mayhavebeen delayed in reaching equilibrium with the environmental fission products. Body burdens of gamma-emitting fission products (such as '*'Cs and "*Zn) were measured in a whole-body counter and checked by radiochemical analysis of urine specimens. Thelevelsofinternal contamination per unit weight appeared to be about the samefor juveniles as for adults, male and female. Wide variations in levels of contamination were found, apparently due to differences in diet, metabolism, and age. Body burdens of “Sr were estimated from urinary excretion as determined by radiochemical analyses. Both the external dose measurements on R.ongelap Island and the 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 whenthe people returned there in 1957. The '"Cs body burden in 1958 was about 0.68 Ci, 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 uCi. The mean bodyburdenof "*Zn estimated from wholebody counting data was, in 1958, after the return to Rongelap, 0.36 uCi, 8 times as hiv as in 1957, and 0.44 uwCi in 1959. In 1961 the mean '''Cs approaching equilibrium with theirenvironment. The *°Zn level dropped to 0.071 Ci in 1959. With a larger detec‘or and a longer counting time than previously employed, it was possible to identify and quantify “°Co for.the first-gne in these people; the mean level of “Co was about 11% of the *°Zn wasstill present after thesubtraction of *°K and the above radionuclides from the total spectrum. The meanlevel of urinary excretion of *’Sr was 7.2 pCi/] or 14% higherX%han measured in the 1959 medica: survey,4962 the mean urinary “Sr level was 114 pCi/g Ca, giving an estimated body burden of 12.0 nCi. Analysis of bones from the deceased Rongelap woman (1962) gave an estimated body burden of 11.4 nCi. These levels represent abouta6-fold increase in *’Sr over the 1958 levels.The levelsof *’Sr in 1962 and 1963 hovered aroundthe 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 popalation at large). It thus appears that body burdensof *’Sr have 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 Isiand. The possible relation of internal absorption of radioiodinesinitially in the fallout to the recent development of 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 showed 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-