INTRODUCTION On March |, 1954, at Bikini Atoll, BRAVO, the first of six nuclear weapons tests in the Castle series, was detonated. The BRAVO device caused substantial surface contamination on inhabited atolls within a 2,000-square-mile area. The contaminated region was cigar shaped and included Ailinginae, Rongelap, Rongerik, and Utirik Atolls which lay east of ground zero at distances from 60 to 300 miles. The fallout on Rongelap, initially visible at H+6 hours, had thinned out to the extent that it was no longer seen at H+l10 hours (G162). On March 3, 1954, the 64 residents of Rongelap Atoll and 18 residents of Sifo Island, Ailinginae Atoll, were evacuated. 157 Utirik Atoll residents also took place. On March 3 and 4, evacuation of During the first few weeks and at least once every year from 1957 to the present, a Brookhaven National Laboratory medical team, organized by the Department of Defense and by the Atomic Energy Commission and its successor organizations, has provided medical examinations to monitor the health of the persons initially affected by the fallout from the nuclear testing program, plus a control population. Reports of their findings are given in Cr56, Co58, Co59, Co60, Co62, Co63, Co65, Co67, Co70, Co75, and Co80. The Utirikese and Rongelapese returned to their home atolls in June 1954 and in June 1957 respectively. The earlier repatriation of Utirik Atoll was based on the low level of external radiation exposure measured after the initial 3-month observation period (March to June 1954). The Utirik population was not examined by a Brookhaven medical team until March, 1957, when 144 people received comprehensive physical examinations. vey, two men, removed Following the 1957, medical sur- from Utirik for medical reasons, were whole-body counted at Argonne National Laboratory and provided urine samples for radiochemical anal. 137 ysis of Cs. oe . toe Four persons visited Argonne from Rongelap and, in addition,