that direction. Other radioisotopes that have been found in soil samples but not in marine organisms are antimony-125 and europam-55 (Palumbo and Lowman, 1958). On page 526 of the report of the 1957 Hearings the suggestion was made that the concentration of various radioactive substances in different parts of marine organisms should be considered because there are marked differences and in the case of some marine organ- isms not only the flesh but the skin, viscera and bones are eaten. The data on one fish that was given is now supplemented by the results of counting 693 specimens collected over a period of 19 months at Eniwetok Atoll (Welander, 1957). The average values by tissues for beta radioactivity based on the per cent of total radioactivity for the tissues counted are as follows: skin muscle bone liver viscera 8% 1% 8% 23% 60% Surveys to determine the geographical and biological distribution of fallout in the ocean during and after Operation Hardtack in 1958 were carried out in a similar fashion to the surveys for Operation Redwing in 1956 (Donaldson, 1956; Seymour, 1957). Plankton continues to be the most sensitive indicator of radioactivity in the sea with concentration factors ranging from one thousand to several thousand. The distribution of fallout in the sea a month after the conclusion of the testing program can be defined from the