21 SUMMARY The concepts on the uptake and concentration of fallout by marine organisms that were presented at the 1957 Hearings are basically unchanged. The greatest emphasis of recent studies has been to identify all of the radioisotopes in the samples. The following observations in an area of local fallout, the Eniwetok Test Site, have been made: (1) Of the three long-lived fission products, cst37, and cel 44 only the latter is found in marine organisms. present, Sr 90 occurs at low levels); by contrast Cs sr?? (If and Sr 90 are found in land forms while cel 44 generally is not. (2) Of the non-fission products radioisotopes of iron, zinc, cobalt and manganese were predominant in marine animals but were much less abundant in marine plants, land plants and land animals. Radiostrontium as stratospheric or possibly intermediate fallout has been measured in the Atlantic Ocean. The data so far available indicates an amount in surface water greater than pre- dicted, but the significance of the difference is questionable because of the limited number of samples. The program at Rongelap Atoll has been enlarged to include basic studies of mineral transport and metabolism in addition to radiation monitoring.