Summary 1, Leveis of activity of the plankton for the eastern Lagoon were sampled nine times in 1954-58. The first observedlevel on Maren 26, 1954, 25 days after detonation of “Bravo" at Bikin4, was, expressed in microcuries per kilogram of planktonic ash, about By mid-December 1954, 1t had decline to 50,. aad. by late 2000. October 1955, to 6. Fallout from the Redwing series raised the July 1256 level to approximately 100. In July 1957 levels were still between 15 and 100, but by early March 1958, shad declined to 0.3. Fallout from the Hardtack series rained juguat 1958.” levels to only 0.8 -4 ye/kg ash, the last observation. Tae decline rate, disregarding the two péake following Redwing and Hardtuck, but including their later residual effects,, was steep with a slope of -3.5. 2. —— o° . O 2 . From the data for the years 1954-57, it was shown that results were nearly twice as consistent when based upon éshas upon wet f weight, and that there was no significant. atererspoe4 in activity between samples taken with fine and coarse meshed neta. . 3. | On the asn weight basis, the levels An 1955, at ailinginae atoll’ were no iiigher than at Rongelap Atoll, ‘whereas theywere higher on the wet weight basis. 4. . no oo Decay slopes of pre-Redwing samples ranged from ~2,6to -2. 4, while the decline slope for the lagoon as a whole over thie period w28 -5.5, so that the decline was more rapid'than the decay.