among the older group. This creates certain difhculties in interpreting someofthe studies to be outlined. 4. The conditionsoffield examinations naturally limit the procedures and methodsthat can beused. Blood volume studies with *'Cr-labeled sodium chromate showeda significant reduction in red cell mass and/or plasma volume. However, there is some indication that Americansliving in the Islands for more than | year mayalso haveslightly lowered values. Tritiated water has been used to establish the relationship of blood volu ‘ae to lean body mass. Further studies on blood volume determinationsare presented later. COMPARISON POPULATIONS Duringthefirst 2 years, two separate groups of Marshallese people were used for comparison, each comparable in size with the exposed Rongelap group and matched for age and sex. However, OTHER BACKGROUND INFORMATION both groups were found to be unstable, with a As mentioned in previous reports, several diffculties were associgted with carrying out the ex- aminations as well as interpreting the findings. 1. The language-barrier made examinations difficult, since very little Englishis spoken by the Marshallese. However, there were sufficient En- glish-speaking Marshallese to assist the medical team in most instances. . 2. The lack ofvital statistics or demographic data on the Marshallese imposesa serious difficulty in interpretation and evaluation of the medical data. Trust Territory officials are attempting to improveregistration of such data. 3. There ts uncertainty on the part of some of the Marshallese as to their exact ages, particularly large attrition rate over the 2 years, which made them unsatisfactory. At the time ofthe 3-yearsurvey, it was found that during the preceding 12 months the Rongelap population at MajuroAtoll had doubled because of the influx of relatives who had come back from otherislands to live with them. These people had been away from Rongelap Atoll at the time of the accidental exposure. This group matched reasonably well for age and sex and was of comparable size. Since the return of the people to Rongelap, however, this group has about doubled in size. Table 2 shows the various Marshallese populations that have been examined since 1954. Table ? Marshallese Populations Examined Since 1954 Group Original number in group Number living (1966) Frequency of exams Subject Nos. Exposed Rongelap* Ailingnae** Lurik 67 19 157 38 15 133 Annual Annual 3-4 years 99 168t Annual since 1957 63tt 60 104 Annual Annual 1- 86 i- 86 2101-2257 U nrxposed Rongelap Rita NTajuro 57 115 1955-1956 1954 only 801-1073 1000-1082 700- 800 Children Conceived After the Fallout Of exposed parent(s) Of unexposed parents “Encludes 3 +7 utero children. **Includes 1 1 utero child. B7- 151 801-1073 tindividuals have been added since 1957 when this group wasfirst available. ttLive births.