RADIOBIOLOGICAL RESURVEY OF RONGELAP AND AILINGINAE ATOLLS MARSHALL ISLANDS OC TOBER-NOVEMBER1955 Introduction During the weapons testing program in the spring of 1954 (Operation Castle), radioactive fallout on some of the atolls was of sufficient intensity to make necessary the evacuation of the native peoples as a health protec- tive measure !} 2,3. The contamination from radioactive material falling upon the islands was especially heavy in the northern portion of Rongelap Atoll and much less at Ailinginae Atoll. The summary statement from the Eighteenth Semiannual Report of the U.S. Atomic Energy Commission outLines the contamination due to fallout as follows. "The highest radiation measurement outside of Bikini Atoll indicated a dosage of 2300 roentgens for the same period (the first 36 hours). This was in the northwestern part of the Rongelap Atoll, about 100 miles from the point of detonation. Additional measurements in Rongelap Atoll indicated dosages, for the first 36-hour period, of 2000 roentgens at 110 miles, 1000 roentgens at 125 miles, and farther south, only 150 roentgens at 115 miles from Bikini "4 In addition to the external radiation problem, there is also interest in the fate of radioactive materials adsorbed or absorbed by the biota and their possible inclusion into the food of the native people, should they be returned to the area. Numerous expeditions have been made tothe atolls to study the problem; -i-