-20- The radiation induction of such changes in the thyroid could conceivably result from injury to the thyroid gland reducing the hormone output and thus calling on the pituitary to secrete a greater amount of TSH. This would give the thyroid picture of hypertrophy in those follicles capable of responding to such hormone and the presence also of atrophic follicles incapable of responding. The development of thyroid nodules following 131, treatment of hyperthyroidism (Sheline et al.) and following x-ray treatment of infants for thymic enlargement (Pincus, Reichlin and Hempelmann) has been reported. The occurrence of radiation-induced mutations would enhance the possible development of malignancy in the irradiated glands. Such a possible development in the Marshallese subjects must be borne in mind. This is particularly true in the case of the children since many retrospective and prospective studies have shown a causal relationship of irradiation of the neck region in infants with the later development of thyroid cancer (Duffy and Fitzgerald; Hempelmann and Fuller; Warren, Alvizouri and Colcock). Simpson, An increased incidence of cancer of the thyroid has been reported in the Japanese exposed to the atomic bomb (Socolow). It is of course not possible to prove the causal relationship of irradiation in the case of cancer of the thyroid in the exposed Marshallese woman but in view of the low incidence of such malignancies in the Marshallese this possibility must be seriously considered. The causal relationship of thyroid deficiency and growth retardation in the children in the more heavily exposed group seems reasonably well established and it is hoped that thyroid hormone treatment will enhance their growth and development. 9001311