HEPATITIS B SEROLOGY IN MARSHALLESE 75 Commission (now the U.S. Department of Energy). To detect unsuspected medical consequences oftheir radiation exposure, a third group of Marshallese has also been followed with medical examinations. This population, composed of Rongelap people who were not on Rongelap Atoll at the time ofthe fallout,is identified herein as the “comparison” group, and the age and sex distribution ofits current members is statistically similar to each ofthe two exposed groups (9). In 1984, sera were collected from 268 persons in the exposed and comparison groups and tested for serological evidence of hepatitis B infection. In addition, 46 children of either exposed or unexposed parents were evaluated to obtain information on the age-specific prevalence of hepatitis B markers. Their ages ranged from 10 to 28 years, in contrast to those in the three exposure categories who were 29 years of age or older at the time of serologic testing. All but three persons tested were residents of one of fouratolls: Rongelap and Utirik are the remote atolls which received the fallout, and Kwajalein and Majuroare larger population centers. Tests for HBsAg, e antigen, and antibodies to HBsAg, core antigen, and e antigen were performed using commercially available radioimmunoassays (Abbott Laboratories, North Chicago, IL). The level of hepatitis B surface antigenemia was estimated by ratio units of the test samples as described in thetest kits. TABLEI Summary ofPositive Serologic Tests for Hepatitis B Surface Antigen (HBsAg), Antibody to Surface Antigen, and Antibody to Core Antigen among 314 Marshallese persons tested Persons with one or more positive tests Persons positivefor 134 180 123 (91.8) 165 (91.7) 20 (14.9) 16 (8.9) Number of By sex Male Female Combined Byage (years) 10-28 29-39 40-49 >49 Byatoll of residence” 314 288 (91.7) 36 (11.5) 46 127 48 93 43 (93.5) 115 (90.6) 43 (89.6) 87 (93.3) 3 (6.5) 14(11.0) 6 (12.5) 13 (14.0) 89 (89.0) 10 (10.0) Kwajalein 100 74 68 (91.9) Rongelap 61 §8 (95.1) Majuro Utirik By radiation exposure group Rongelap exposed Utirik exposed Rongelap comparison Byatoll of residence, excluding Rongelap exposed Kwajalein Majuro Rongelap Utink HBsAg 76 61 70 (92.1) 50 (82.0) 4(5,4) 3 (8.5) 19 (25.0) 2 (3.3) 112 103 (92.0) 21 (18.8) 95 86 (90.5) 10 (10.5) 69 6l 44 76 63 (91.3) 58 (95.1) 42 (95.5) 70 (92.1) 6 (8.7) 4 (6.6) 3 (6.8) 19 (25.0) * Percentage of the total population tested is shown in parentheses. » Three persons resided outside the atolls listed.