regimen in this population, and increased efforts in this direction seem to indicate an improved trend. The favorable effect of the hormone treatment in improving growth and development in some of the growth-retarded children is discussed in past reports (1,27) and in Section IV. It remains uncertain whether the treatment has had an effect in preventing formation of thyroid nodules. Some exposed individ- uals have developed nodules while taking medication conscientiously. 5. lodoprotein Studies In the course of serum hormone measurements to monitor possible radiation effects on thyroid function, it was fortuitously discovered that the native people in the Marshall Islands normally have a serum iodoprotein level higher than that found in Western people, even while residing in the Marshall Islands -- see Table 32 of the 20-yr report (1). The finding of serum iodo- protein in athyrotic Marshallese suggested that this substance arose outside the thyroid gland. It was postulated that it might be iodoalbumin or other serum protein iodinated by blood leukocytes in the context of chronic inflammatory disease such as parasitic infestation. There is still no proof for this hypothesis. In 1973, serum thyroglobulin was measured in a number of individuals from various groups; the findings are summarized in the 20-year report (Figs. 41 and 42) (1). Thyroglobulin levels were the same as in the U.S. nor- mal population and thus could not explain the elevated serum iodoprotein. In addition, it was found that Rongelap and Utirik people who had had thyroid surgery tended to have lower than normal serum thyroglobulin levels. This may have been the result of thyroid gland removal or more likely of suppression by thyroxine therapy. The major significance of the elevated iodoprotein is that it was responsible in the early phase of the Marshall Island surveys for failure to recognize hypothyroidism. The serum protein bound iodine was the routine screening test at that time. Since the development of radioimmunoassays for T,, T3, and TSH and their application in the surveys, this problem is no longer important. D. Discussion of Thyroid Findings The most definite and widespread late effects of exposure to fallout in the Marshallese have been related to the latent development of thyroid nodularity, benign and malignant; the development of nodules in two children exposed in utero; growth retardation in some of the children; and, more re- cently, the finding of hypofunction in some exposed people with and without evidence of other thyroid abnormalities. The role of radiation exposure in the etiology of thyroid abnormalities in the Marshallese seems clear. There are no known goitrogens that might play a role, and the iodine intake of these people is adequate as indicated by adequate levels of iodine in food sources and in the urine. During the past five years thyroid examinations of unexposed populations of Marshallese have been expanded for comparison with those exposed to fallout. The results have been important in the evaluation of findings in the exposed people. As discussed in Appendix I, the incidence of thyroid abnormalities in these unexposed Marshallese does not appear to be very - 76 -