42 of the reacting antigen was under genetic control. Individuals with a dominant gene designated Ag* in single or double dose (genotypes 4g*/4g*, Ag*/Ag) were reactors [phenotype Ag(a+)] and those homozygous for the recessive allele Ag non- reactors [Ag(a — }|. The antigen or antigens that react with the antibodies present in the serum of the frequently transfused patient are serum low density 8-lipoproteins.'’ A serum from a second patient (I.M.), the New York antiserum, was also found to react with a low density 8-lipoprotein. Preliminary family studies indicated that reactors were homozygous or heterozygousfor a second gene, while nonreactors were homozygousfor the alternate recessive allele. Immunologic, genetic, and population studies showed that thelipoproteins selected by the two antisera were antigenically distinct and controlled by different genes.'* exposed and unexposed of ages <15 and >15 years, living on Rongelap, Ebeye, and Utirik. Sr°° urine levels for 1963 and 1964 have not increased over the 1962 levels. In 1962, the mean Sr®° values from the individual adult 24-hr samples were 12.45 pC/I or 114 pC/g Ca. From these values, on the basis of previous calculations.* '° the body burden was estimated as 12.0 muC for adults and 28.4 muCfor children. On the same basis, the estimates for 1963 body burden levels of Sr®* are 11.3 muC (adults) and 21.8 muC (children); and for 1964, 10.7 muC (adults) and 23.1 muC (children). As shown in Table 23, the levels of both Cs'*” and Sr*° are lower for the people living on the uncontaminated island Ebeye at Kwajalein Atoll. Thus the return of the Rongelap people to their total results compared with those on several other homeisland was reflected in annual increases to 1962 in estimated body burdens of Sr®° based on urinary excretion values. The annual estimates in myuC for adults were as follows: 2.0 in 1958; 6.0 in 1959; 6.9 in 1961; 12.0 in 1962; 11.3 in 1963; and much higher frequency of C.deB. antiserum reactors and a muchlowerfrequency of New York 5 to 6% (adults) to about 10% (children) of the maximum permissible concentration (MPC) of “Sera collected from the inhabitants of Rongelap Atoll in 1962 were tested with both the C.deB. (anti-Ag(a+)| and the New York antisera. The populations are shown in Table 22. There is a 10.7 in 1964. The present body burdens are about antiserum reactors in the Rongelap population Sr** (200 muC)for non-industrial populations.It on differences in past or present selective forces the people living on Rongelap Island, and the previously estimated equilibrium value of 23 muC than in U.S. whites and Negroes. The reasons for these differences are not known, but may depend which affect the balance of the polymorphisms. “Because of the lower frequency of New York antiserum reactors, the Rongelap population was useful for family studies. From these studies it was tentatively concluded that reactors with the New York antiserum were either homozygousor heterozy gous for a dormant gene, and nonreactors were homozygous for its alternateallele.” Radiochemical Analyses of the Urine. Determinations of body burdens of gamma emitting isotopes (principally Cs'*’ and Zn**) by wholebody gammaspectroscopy were not done during the past two surveys. Data in 1961, by that tech- nique, indicated that the body burdensof Cs'*’ were notsignificantly different from those of two years before, and Zn®levels had dropped bya factor of about 10. It was decided, therefore, to defer whole-body counts until the 1965 survey. Results of radiochemical urine analyses for Cs'** and Sr? on 38 urine samples for 1963 and 27 samples for 1964 are presented in Tables 23 and 24. The data are divided into the following groups: appears now that equilibrium with the environmental contamination of Sr*° has been reached in will not be reached. No bone samples were obtained from autopsy material during the past two years for Sr®* anal- ysis. Estimates of body burdens from previous analyses of bone samples had shownfairly good correlation with those obtained from urine analyses. In view of the paucity of the previous data on Cs'37 urinary levels, it is difficult to interpret the present levels in terms of body burden. However, the levels are generally less than the mean 1958 Cs'3* urinary level of about 4 nC/I. This is in accord with the finding by gammaspectrographic determinations that the whole-body burdens of Cs'37 in 1961 had not increased. Analyses of three coconut crabs for Sr®° and Cs}3? are shown in Table 25. Though the levels of Sr*° (pC/g Ca) are lower thanin the crabs analyzed in 1962, they are still sufficiently high to necessitate continuation of the ban on their consump- tion by the people of Rongelap.It is interesting that the Cs'*" levels are also quite high in these crabs.