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 606, 6575 and 13765, For 137 6, 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 055 and 239, 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 5356 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 compari- son 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 (ICRP74). Due to the paucity of early measurements of activity in Utirik residents 0 . (see Table 2), their 6 Co, 2395, and Fe 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