ABSTRACT Studies of the radioactivity in reef fishes of Belle (Bogombogo) Island, Eniwetok Atoll, were made during a pertod of about one year following the atomic detonations in 1954. Thirty-four different collections were made and 693 specimens were analyzed to determine activity. the trend or decline of radio- The decline of radioactivity during the period under study was generally similar in all species. The rela- tive amount of radioactivity per gram of tissue was greatest in the alimentary tract, with the liver, having successively lesser amounts. vailed throughout the period. skin, bone and muscle This relationship pre- The rate of decline was great- est during the first 100 days, with a loss of 90 per cent of the radioactivity during the period. Studies were made on the variation of total radioactivity in the tissues and species, on comparisons of the amount of radioactivity in the species and in their food, and on comparisons of the decline of radio- activity during the period with the decay of radioactivity in tissues collected soon after the shots.