ll contributed an average of 29 per cent of the total radioactivity. The remaining 71 per cent was contributed by the non-fission radioisotopes zn°>, 692719860 F e> and Mn>*, cobalt, and iron accounted for averages of 24, Radioactive zinc, 26 and 21 per cent, respectively,of the total radioactivity; mn>* was present in trace amounts (Lowman, 1958). The results of analysis of four of the samples are given in Table 2, In the Hardtack plankton samples the presence of radioactive tungsten (wi 85, was striking. Plankton samples with wi85 were found in three areas and contributed as much as 83 per cent of the total radioactivity. Plankton taken outside of these areas did not contain radiotungsten nor was it found in any plankton samples collected three weeks later in the same area, corrected for the rate of advance, where wr 85 was found originally 1959). (Lowman, The assumption based on this and other evidence is that tungsten occurred as an external contaminant and that little was taken up biologically. The analyses of four of the 1958 plankton samples are also given in Table 2. The 1958 plankton sample was of fresher fallout material which accounts in part for the difference in the radioisotopic composition between the 1956 and 1958 plankton samples. From the measurement of the radioactivity in plankton, and other organisms in the sea, fish it is evident that the organisms, especially plankton, play an important role in the translocation