-22- Fe is the dominant radioisotope in tissues of fish from Eniwetok and Bikini Atolls. Mn°4 is often present in fish tissues but only in small amounts. Some differences in radioisotopic content of certain organs in the same fish have become evident. Bone, for example, differs from most other tissues in lacking Co°”, Co98) and Co80, although considerable amounts may be present in the muscle and liver of the same fish. If the radioisotopes in Table 7 are used and the half lives weighted by either the per cent of total activity or the d/m/g wet weight, the estimated generalized decay of the radioactivity in the sample indicates an approximate 380-day half life for the period between the summer of 1957 and the summer of 1958. An estimation of the biological half life of the radiosotopes in the fish of the Rongelap area would be even more speculative. However, if the comparisons of the decline and decay in Figures 1 and 2 are indicative, it would appear that the biological half life igs longer than that estimated for physical decay in the previous paragraph. It would be of value to know the biological half life of each of the radioisotopes in the Rongelap environment. Ap! LVN Ke