RADIONUCLIDES IN PLANKTON NEAR THE MARSHALL ISLANDS, 1956 Introduction During the summer and fall of 1956 members of the Applied Fisheries Laboratory conducted two surveys in the region of the Pacific Ocean bounded by the Marshall, Caroline, and Marianas Islands. The purpose of the surveys was to measure the levels of radioactivity in the water, plankton, and fish and to determine the westward boundary of the contaminated area. The first survey was made June 11-21, 1956, during the weapons testing period and included 53 collection stations in the ocean 11° N to 14° N and 159° E to 1669 E. The re- sults were reported in U. S. Atomic Energy Commission report UWFL-46 (6). The second survey conducted from September 1- 20, 1956, about six weeks after the conclusion of the weapons tests, included 74 stations between 9° N and 15° N and DOE ARCHIVES approximately 145° E and 166° E (Fig. 1). The findings were published in U. S. Atomic Energy Commission report UWFL-47 (21). Chemical separations for fission products, cobalt, and zinc were made on a limited number of samples from both surveys, the results of which were reported in the latter report (21). According to these data fission products contributed a major