cell mass and/or plasma volume. However, there amongthe older group. This creates certain diffculties in interpreting someofthe studiesto be outlined. Islands for more than | year mayalso haveslightly limit the procedures and methods that can beused. Blood volume studies with *'Cr-labeled sodium chromate showeda significant reduction in red is some indication that Americansliving in the lowered values. Tritiated water has been used to establish the relationship of blood volumeto lean 4. The conditionsoffield examinations naturally COMPARISON POPULATIONS body mass. Further studies on blood volume de- terminations are presentedlater. OTHER BACKGROUND INFORMATION As mentioned in previous reports, several difficulties were associated with carrying out the examinations as well as interpreting the findings. 1. The language barrier made examinations difficult, since very little English is spoken by the Marshallese. However, there were sufficient English-speaking Marshallese to assist the medical team in mostinstances. 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 is uncertainty on the part of some of the Marshallese as to their exact ages, particularly During thefirst 2 years, two separate groups of Marshallese people were used for comparison, each comparablein size with the exposed Rongelap group and matchedfor age and sex. However, both groups were found to be unstable, with a large attrition rate over the 2 years, which made them unsatisfactory. At the time of the 3-yearsurvey, it was found that during the preceding 12 months the Rongelap population at Majuro Atoll had doubled becauseofthe influx of relatives who had come back from other islands to live with them. These people had been away from Rongelap Atoll at the time of the accidental exposure. This group matchedreasonably well for age and sex and was of comparablesize. Since the return of the people to Rongelap, however, this group has about doubledin size. Table 2 shows the various Marshallese populations that have been examined since 1954. Table 2? Marshallese Populations Examined Since 1954 Group Original number in group Number living (1966) Frequency of exams Subject Nos. Exposed Rongelap* Ailingnae** Uurik 67 19 157 58 15 133 Annual Annual 3-4 years 99 168+ Annual since 1957 l- 86 i- 86 2101-2257 Unexposed Rongelap Rita Majuro 57 115 1955-1956 1954 only 801-1073 1000-1082 700- 800 Children Conceived After the Fallout Of exposed parent(s) Of unexposed parents *Includes 3 127 utero children. **Includes | 17 utero child. 63tt - 60 104 Annual Annual 87- 151 801-1073 tIndividuals have been added since 1957 when this group was first available. ttLive births.