not be discussed here. A reassessment of thyroid absorbed dose from the initial 1954 exposure is currently being made and will be reported in a separate study. Since April 1978, the bioassay program and whole-body counting studies have been performed by members of the Safety and Environmental Protection Division of Brookhaven National Laboratory. Reports of their findings may be found in Gr77a, Gr77b, Le80a, Le80b, Mi80, Mi8l and Na80. The report by Lessard (Le80b) contains more detail on the development of the equations used here. The Utirik and Rongelap inhabitants were returned to their home atoll in June 1954 and in June 1957, respectively. The earlier repatriation of Utirik Atoll was based on the low measured level of external radiation exposure over a 3 month observation period. The Utirik population was subsequently examined by a Brookhaven medical team during 1957; 144 people received comprehensive physical examinations. In 1957, the Rongelap inhabitants were also returned to the their atoll to occupy new homes, community structures and other facilities which had been constructed during their three year residence at Majuro and Kwajalein Atolls. Following the 1957 medical survey, measurements were made on two men from Utirik Atoll using the whole-body counter at Argonne National Laboratory. Radiochemical analyses of their urine samples were also made. Four persons from Rongelap Atoll also visited Argonne for whole-body counting in 1957. In addition, pooled urine samples from both atoll populations were analyzed radiochemically for 137 Cs and 90 Se The body burdens measured at Argonne National Laboratory were corrected for ten days of biologic elimination and radiologic decay in order to estimate the body burden while living on the atoll. Starting in May 1958, Conard and Cohn (Co59), measured whole-body levels of i 37 . . . Cs, $370, and 6005 in about 100 Rongelap adults, adolescents and juveniles