exposure, the results on four other exposed, unoperated individuals had a single TSH determination > W/ml. All of these individuals had TRH-induced TSH responses between 30 and 35 wW/ml. Therefore it is possible that in the next few years additional individuals will be identified who meet the criteria for biochemical thyroid dysfunction. None of the subjects with elevated serum TSH had detectable antithyroglobulin or thyroid antimicrosomal antibodies. 3. Thyroid Abnormalities in Cases Exposed In Utero In the Rongelap group, exposed to 175 rads of whole-body radiation, there were three people exposed in utero. Benign tumors of the thyroid have been removed from two of these: adenomatoid nodules removed at age 24 from a male (No. 83) exposed at the end of the second trimester, and a hyperplastic nodule removed at age 26 from a male (No. 85) exposed at the end of the first trimester. A female (No. 86) exposed in the first trimester has developed no detectable thyroid abnormalities. In the Ailingnae group (69-rad whole body exposure) there was one exposure at the end of the first trimester, and in the Utirik group (14-rad whole body exposure) there were six in utero exposures. No thyroid abnormalities have appeared in any of these cases. The total thyroid doses in these cases cannot be accurately estimated. The function of the fetal thyroid at the time of exposure is an important fac- tor in such estimations. A few reports are available concerning function of the fetal thyroid gland at various stages of gestation (134-137). The gland is thought not to accumulate iodine before the 12th week of gestation, but thereafter becomes increasingly active, and at birth is more active than in the adult or child. In case No. 83, at the time of exposure -- 22 weeks gesta- tion —- the thyroid was probably functioning sufficiently to have absorbed a Significant amount of radioiodines from the mother's blood. In case No. 85, it is unlikely that the thyroid was sufficiently functional at 12 weeks gestation to have absorbed a significant amount of radioiodines from the mother, and the development of the thyroid nodule may have been associated with the gamma exposure. Data on the time of gestation and degree of exposure in the six Utirik cases are uncertain, but their thyroid doses both from whole-body and from possible radioiodine exposure would have been far less than those of the Rongelap group, and this is consistent with the lack of findings in that group. Neither of the in utero exposed children who developed thyroid nodules showed any impairment in growth and development (see Section IV). No. 83 had an elevated TSH level prior to surgery, but without evidence of clinical hypothyroidism. The thyroid status of the mothers of the two in utero cases who developed thyroid nodularity is of interest. The mother of No. 83 was ex- posed at age 15 to an estimated thyroid dose of 175 rads gamma radiation plus 250 rads from radioiodines and developed a thyroid cancer at age 32. She showed evidence of biochemical hypothyroidism prior to surgery (Section IX.C.2.). The mother of No. 85 was exposed at age 17 to an estimated thyroid dose of 175 rads gamma radiation plus 160 rads from radioiodines. She has not developed nodularity of the thyroid gland, but hypertrophy of the pyramidal lobe at age 43 was noted. A number of cases of myxedema have been reported following in utero expo- sure during treatment of the mother with large doses of radioiodines for hyperthyroidism (mCi amounts, compared with probable MCi amounts in the - 74 -