= 3- The hematological surveys continue to show considerable fluctuation in the year-to-year mean levels of leukocytes in both the exposed and unexposed groups. The mean leukocyte level of the exposed group showed a decrease at the 1960 survey compared to 1959 (no unexposed people were examined). The reasons for these fluctuations are not apparent. At five years post-exposure (1959), the exposed people still had mean platelet levels 10 to 15% below those of the unexposed group, but in 1960 the lymphocyte levels for the first time equaled those of the unexposed group. The mean erythrocyte levels were slightly lower in the exposed people but a general anemic tendency exists in all Marshallese, both exposed and unexposed. The fact that some of the blood elements in the exposed group have not yet returned to the levels of the unexposed group raises the possibility that a residual radiation effect on the bone marrow persists, but other, not immediately apparent, factors may be involved. Radiomuclide body burdens of Cs/37, zn©5 ana sr9° were evaluated by measurement in a whole-body counter or by estimation from radiochemical analyses of the urine. The mean body burdens for 1959 were: Cs137 = 0.57 «1c; mmO5 = O.44c; and Sr90 = 6.0%c. The body burdens of 2n©5 and Sr90 continue to rise but at decreasing rates, whereas the level for Csl3T appears to have reached equilibrium and now to be diminishing. little or none of the body burdens of the exposed group appear to be due to the initial exposure, since at present there is little difference between the levels of the exposed and unexposed populations living on Rongélap Island. This may be explained by the fact that additional weapon testes held in the area have deposited additional fission products into the environment, and the fact that certain staples of diet are imported and, hence, the people are not living in a "closed enviroment." Consequently, it may never be possible to equate body burdens with enviroumental contaminations. In any case, the body burdens are now and will be of small significance in terms of radiation hazards. Judging from the Japanese populations being studied by the Atomic Bomb Casualty Commission at Hiroshima and Nagasaki, the next five years will be the critical period for the development of leukemia in the Marshallese. Since animal experiments indicate that still other late effects may occur in man such as premature ageing, shortening of life span, increase in degenerative diseases, genetic changes, etc., contimued careful examination of these populations is in order; all effects should be documented and therapeutic procedures instituted wherever possible, should such effects develop. In addition, the relation of the enviromental contamination on Rongelap to the body burdens of radionuclides of the people living there, imperfect though it is, warrants close study. The United Nations Scientific Committee on the Effects of Atomic Radiations now reviews these yearly surveys.