Autoimmunethyroid injury: disease, but are useful as a screening test. Hypothyroidism is often quite subtle and difficult to diagnose, and any markerthat mightidentify a population at risk for subsequent hypothyroidism would be clinically useful. Therefore 231 Marshallese sera collected in March 1987 were tested for the presence of antithyroglobulin and antimicrosomal antibodies in the laboratory of Dr. Harry Maxon. Fifty-five sera were from the Rongelap-ex posed, 94 were from Utirik-exposed, and 82 were from the Comparison group. Two persons had data consistent with the diagnosis of autoimmune thyroid disease (Table 4), and both were in the Comparison group. One was a 38-year-old woman who had Grave's disease with hyperthyroidism diagnosed in 1980 that was treated with 131]. Her serum contained both types of antibodies in 1980 as well as in 1987. The other person, a 32-year-old woman, had an antithyroglobulin antibody level of 35 U/l. She has Sheehan's syndrome,present since 1975 following postpartum hemorrhage. In addition, six persons had nondiagnostic but slightly elevated levels of antithyroglobulin antibodies, two from Rongelap and four from Utirik. None have clinical evidence of autoimmunethyroid disease, although three have had thyroid lobectomies for benign nodules. The lack of evidence for an increase in autoimmune thyroid disease among the exposed Marshallese is consistent with the findings of Radiation Effects Research Foundation studies. In a 30-year followup of personsless than 20 yearsof age at the time of exposure to the atomic bomings in Japan, no difference was detectedin the preval- Radiation-induced thyroid hypofunction, diagnosed in fourteen exposed Rongelap individuals, was not found to be increased among Japanese A-bomb survivors. This difference reflects the larger dose absorbed by thyroids of the Marshallese, a consequence of ingestion of radioiodines. The question arises as to whether thyroid hypofunction in the exposed Marshallese is a consequence not only ofdirect radiation injury, but also of immunologic damage. Immunologic studies by the Radiation Effects Research Foundation found that Japanese A-bombsurvivors greater than fifteen years of age at exposure had a significant decrease in mixed lymphocyte culture response that was inversely related to radiation dose (Akiyamaetal., 1987), and lymphocyte responses to phytohemagglutinin decreased more rapidly with age in persons who received more than 200 rad. However, the immunological responses of aging Japanese A-bomb survivors do not appear to have been affected by radiation exposure (Bloom etal., 1988), nor does there appearto be an increase in diseases associated with autoimmunity in the exposed Japanese population. Immunologic damage to the thyroid is mediated, in part, by circulating autoantibodies that are apparently cytotoxic. Antimicrosomal antibodies are important in the diagnosis of autoimmune thyroiditis, a disease process commonly progressing to hypothyroidism (Frey, 1987). Antithyroglobulin antibodies are far less specific an indicator of thyroid autoimmune TABLE 4: ANTITHYROID ANTIBODIES IN THE DIFFERENT RADIATION EXPOSURE GROUPS. Exposure group (n) Rongelap (55) Utirik (94) Comparison (82) Elevated antithyroglobulin antibodies* 2 4 2** Percent elevated 4% 4%, 2% “ The levels ranged between 6 and 11 U/1, with normallevels being < 5 U/1. ** One subject had elevated antimicrosomal antibodies (35 U/1) and a history of Grave’s disease with hyperthyroidism. C7 a cy 13