distant metastases, the clinical prognoses for these individuals remains highly favorable. Although fourteen of these tumors were classified morpho- logically as malignant neoplasms (carcinomas), either occult or overt, it should be emphasized that the lay term "cancer," with its ominous implications, should not be applied to such clinically benign lesions, a point well noted by others (255,259). 2. Thyroidal Hypofunction Criteria used in defining biochemical thyroid function were developed from findings in the control and exposed Utirik populations presented in Table 6.* In the initial series, an upper limit of 3 LU TSH/ml serum was selected, since baseline studies in 25 unexposed Marshallese who were clinically and biochemically euthyroid yielded a mean value of 2.0 uU/ml (SD = 0.73) with a range of 0.5 to 3.0 W/ml. Serum TSH concentrations in this group after injec- tion with 500 ug of TRH averaged 11.5 wU/ml (SD = 4.5) with a range of 4.7 to 20.0 wyU/ml. These results are similar to those obtained in other normal populations with respect to both basal TSH and TRH-induced TSH release (111,130,131). Table 6. Number of subjects with elevated serum TSH concentrations in control and exposed Marshallese populations (1975-1979). Initial Series Sub jects Control (unexposed Marshallese) Tested once 115 Single TSH >3 wWU/mi 11 Second Series Tested two Two TSH values or more times >6 wW/ml (102%) 67 Utirik exposed 99 12 (12%) 101 Rongelap-Ailingnae exposed 43 11 (26%) 36 (thyroid dose <95 rads) (No prior surgery) 2 (3.0%) 0 7 (19%) As shown in Table 6, only 10% of a control population of 115 had serum TSH concentrations >3 wU/ml. In the the Utirik population exposed to relatively low doses of radioiodine, 12% had single TSH values >3 w/ml. These results suggested that there was no difference between these two populations with respect to the prevalence of elevated serum TSH. In the exposed (but *Data from the exposed Utirik group were combined with the data from the unexposed group because that group showed no evidence of thyroid hypofunction associated with the low doses to their thyroids. ~70-