infrared heat lamp, 110 c/m after Maming and 4 c/m after covering with aluminum foil 4.7 mg/cm? in weight. A total correction factor of 112 was used (based on a secondary Fe55 standard obtained from Dr. C. A. Finch, University of Washington) to convert to disintegratione per minute. The radioisotopes of zinc, cobalt and manganeee were identified by their gamma energies and the disintegrations per minute were calculated from the gamma spectrum curves of the different fractions. Radiostrontium was not detected in the citrate fractions where it would be expected to occur. Radiochemical precipitation determinations revealed the presence of sma}! amounts of radiostrontium in the bone of fish collected at Kabelle Island. No radiostrontium was detected either in the liver or muscle of any of the fish taken at Ailinginae or Rongelap Atolls or in the bone of fish from Enibuk Island or Rongelap Island. Table 6 con- tains data on the Sr99 content in fish tissues collected during and since 1954 at Rongelap Atoll by this Laboratory. Except for traces of gr90 in goatfish and reef fish bone from the Kabelle Island 1957 collections and in bonito bone from the 1955 collections at Labaredj, no radio- strontium has been detected in the fish tissues. A summary of the data on the radioisotopes obtained from the liver tissue sample of reef fish from Enibuk Island is contained in Table 7. In total radioactivity, Zn85 contributed about 40 per cent, Co2”?, C058,