ABSTRACT Radiochemicsl separations were made on plankton samples collected in and west of the Eniwetok Proving Ground in September 1956. Ion exchange resin column and precipitation technicues were used. Fission products, mainly Zr99-Nb95 and Celt4_ppl4d contributed an average of 29 per cent of the total radioactivity. The remaining 71 per cent of the activity was contributed by the non-fission radioisotopes zn©5, C057,58,60, Fe55 and Mn>4. and Radioactive zinc, cobalt, iron accounted for averages of 24, 26 and 21 per cent respectively of the total radioactivity. in trace amounts. mn54 was present Variations in ratio of occurrence for the different non-fission products with change in geographical location was observed. Relatively high levels of zn©5 were centered in the area near Bikini and Eniwetok Atolls. The area of high levels of radioactive cobalt and iron in comparison to zn©5 was located approximately 480 miles west and slightly north of Eniwetok Atoll. Oy DOE ARCHIVES