RESULTS Body Burden Data and Urine Activity Concentrations The average body~burden data for adults since their return to Rongelap and Utirik Atolls are presented in Tables 1 and 2. ‘In these tables, the zero day or day of return for Utirik was nearly 1,000 days prior to the zero day or day of return for Rongelap. Directly measured body burdens were listed for 6c, 6570 and 137 Cs. For 1376, an initial rise in body burden and a subsequent general decline was apparent. These data were plotted in Fig. 2 along with their stan- dard deviation and standard error. Conversion of adult average 905. and 2395, urine activity-concentration data was done as indicated in the methods section in order to derive a body burden for these nuclides. Average data were listed in Tables 1 and 2 and plotted in the case of 90. (see Fig. 3). obtained from Beasley (Be72). The body burdens listed for 555 were The methods used to derive 5556 body burdens from blood measurements were given in Be72. The most recent whole-body counting data available (1981) are presented in Table 3. Analysis of the data indicated that 1376, adult average body burdens at Rongelap and Utirik were from 40 to 90 times greater than those of a comparison population at Majuro, a southern atoll which received little fallout from testing (Le80c). The 40, levels and corresponding potassium content were in close agreement with naturally occurring values developed from data in ICRP 23 CICRP74). Due to the paucity of early measurements of activity in Utirik residents (see Table 2), their 8000, 23954, and re body burdens were estimated by comparing nuclide ratios for Utirik and Rongelap residents. The measured body burdens for these nuclides in Rongelap residents and the observed atoll-to-atoll 12