-55Fe-> and znd were the principal radioactive constituents, Mn34, Cool, C038, and Co with 60 contributing the remainder of the activity. 6, In fish liver samples collected at Belle Island, Enti- wetok Atoll, May and June, 1954, Fe-> accounted for 95.3 per cent and gn©5 3.1 per cent of the total activity. Min >4 Col, and C900 also were detected, 7. ‘The pattern of cistribution of the transition elements manganese, iron, cobalt, and zine in the plants and animals at the Pacific Proving Ground is as follows. In general, they are present in the sea and not on the land, in marine animals and not in marine piants. Few or none of the radioactive transition elements are present in island soil, in plants growing in the soil, or in the herbivorous field rats (Rattus exulans), ever, in the plankton, How- the marine invertebrate filter feeders and omnivores, and in the fishes, the above named isotopes are present and may contribute up to 100 per cent of the total radioactivity.