12 and movement of radioisotopes in the sea. The ability of plankton organisms to rapidly acquire a large part of the radioactivity in the sea and to make diurnal vertical migrations from the relatively fast moving and well mixed surface layer of the ocean to the slow moving stratified water layers of the deeper ocean has been demonstrated. A study of the fundamental processes involved in the translocation of radioisotopes by a plankton population has been initiated and a report of the state of progress of this research was given at the second Geneva conference on the peaceful uses of atomic energy (Ketchum and Bowen, 1958). In addition to the analyses to determine the radioisotopes present in plankton, clams, similar analyses have been made of algae, fish and many of the land plants and some of the land aninals. A few of the Table 2. analyses for algae, clams and fish are given in The results as given in the Table are comparable from one sample to another only in a general way because the specimens have been collected from areas that have received fallout at various times ranging from a few days to ten years. Although the analyses of the land plants and animals are not given, there is a striking difference between the land and the sea in the biological distribution of the fission products and non-fission products sition elements). In general the transition elements iron, (tanzinc, cobalt and manganese are present in marine animals but in very