In addition to the tuna from the Japanese fishery, sixteen yellowfin tuna, believed to be from a single school, were caught off Bikini Atoll in the Marshall Islands in September 1969. Liver samples, not obtainable from the Japanese-caught fish, and light muscle and dark muscle from these fish were analyzed for gamma-emitting radionuclides, iron-55 and stable iron. The samples were counted for 900 minutes each with 3-inch x 3-inch Nat(Tl) analyzers, crystals used in conjunction with 256-channel Spectrum reduction was done by Schonfeld's method of least squares, (1965) and all values were corrected for decay to the date of collection. Iron-55 was separated and purified by a combination of solvent extraction and electrodeposition techniques Beasley, 1967). Recoveries generally exceeded 90%. (Palmer and Counting was done by X-ray spectroscopy with a proportional counter used in conjunction with a multichannel analyzer. Some duplicate samples were analyzed by different persons using different methods, ard the results were in close agreement. RESULYS The values for 55 . tuna had a wide range. Fe, The ranges for dark muscle were to 1600 pci/g dry weight; oo. aclivity, . toes tos . stable iron and specific activity in . 0.02 to 8.6 nCci iron, 49 to 500 ppm; 35 Fe/mg Te. 55 Fe, and specific 3.3