tha Ty Radiation-Associated Thyroid Carcinoma 251 ment following exogenous TSH stimulation, and by endogenous TSH response to thyrotropin releasing hormone (TRH) \ It has not been feasible to do thyroid scans in the islands. The results indicated the following: 1) ‘Prior to surgery some subjects with nodules had reduced T4 levels. 2) Following surgery nearly all patients, in spite of attempted thyroxine therapy, exhibited reduced function on occasion, which showed that the remaining tissues were not capable of maintaining a euthyroid state. 3) Recently about 50% of the ex- posed Rongelap people showed biochemical hypothyroidism without clinical evidence of thyroid disease, a finding that probably portends trouble ahead. RISKS FOR RADIATION-INDUCED TUMORS IN THE MARSHALLESE The data on the Rongelap people in Table 4 indicate that, on a risk per rad basis, the incidences of benign and malignant thyroid lesions are about the same for them as for groups exposed to x or gamma radiation, except for the higher risk values for the Utirik adults. Clinical experience suggested that 131] is less effective than x-rays in producing thyroid tumors. This may in part be due to dose rate and the soft beta radjation of that isotope, much of which is wasted in the colloid of the larger follicles not reaching the follicular cells. The higher energy of the short-lived isotopes of iodine (particularly 1321, 1331, ana 155x), resulting in higher dose rate and more uniform exposure of the thyroid, is thought to have been the important factor in increasing the number of thyroid abnormal- ities above that expected from similar doses from 1311 alone (12-13). This reasoning is supported by a number of animal experiments (14-15). Thyroid uptake studies were done by Drs. J.E. Rall ahd J. Robbins at NIH, and by Dr. H.L. Atkins at BNL; RIA studies, by Dr. P.R. Larsen at Peter Bent Brigham Hospital and by Drs. J. Robbins, M. Gershengorn, M. Izumi, and J.L. Baulieu at NIH.