75 posure under extremeconditions, with no corrective measures taken to reduce internal absorption of radioisotopes prior to evacuation of the exposed people from thefallout area. It did not involve the contaminated pasture-cattle-milk cycle, which might be an important pathway ofradioiodine to manin othertypes of accidents (such as the Windscale accident).176 Civil Defense planning can providefor several measures that will reduce the hazard of thyroid exposure dueto radioiodine absorption and thus largely preclude the degree of thyroid injury sus- tained by the Marshallese. Since the hazard from radioiodine is acute for a period only of days, early protective measures are extremely important. These include avoiding inhalation of radio- iodines by shelter protection; consuming food and wateronly from closed containers; feeding cowsin contaminated areas protected fodder; and tem- porarily withholding contaminated milk supplies and diverting them into processed products with a shelflife longer than thelife of the isotope. The addition ofstable iodine to food or water during the first week woulld provide a relatively inexpensive method of reducing thyroid uptake of radioiodines by isotope dilution and saturation with non-radioactive iodine; this should rarely produce anyseriousside effects and would beofparticular value in children and pregnant women. When exposure of the thyroid has already occurred, prophylactic treatment with thyroid hormone, now being used in the Marshallese, may help prevent developmentof thyroid tumors, and even after tumor development, surgical excision may reduce mortality due to malignancy. The thyroid effects in the Marshallese were not anticipated at the timeofthe accidentor during the early years afterwards. In retrospect this is not surprising, for several reasons. At that time the thyroid was thoughtto be relatively radioresistant, particularly with regard to radioiodine exposure (on the basis of animal studies and diagnostic and therapeutic use of 131I in people), and the calcu- lated thyroid doses in the Marshallese were considered to be below the levels likely to produce tumors. In addition, neither the importanceof the exposure to short-lived iodine isotopesin fallout nor the thyroid dose differential in children due to the smallersize of their gland was fully appreciated. It is quite likely that the final results of thyroid lesions in the Marshallese are incomplete at this time since new lesions are still occurring. The meanlatent period for radiation-induced thyroid tumors maybe as long as 30 years. Cases have been seen as late as 40 years after exposure. Furthermore, on the basis of the present data therisk of developing radiation-induced thyroid neoplasia is probably underestimated, since surgical removal of potentially malignanttissues may have occurred and the hormonetreati:.ent may haveinhibited the developmentof some tumors, althoughthelatter is questionable. As has been pointedout,also, the true carcinogenic potential of the exposure, particularly in the children receiving the higher dose, may have been masked by excessive cellular destruction. The recent finding that subclinical thyroid deficiency is present in some of the exposed people who havenot shownany thyroid abnormalities indicates that the thyroid effects in the Marshallese may not yet be completely manifest, and continued careful surveillance of this population Is necessary. Acknowledgments Because of the broad scope of the surveys and the complexity of operations it would be impossible to acknowledgeall the individuals and organizations that have contributed to the success of the surveys over the past 20 years. We would like, however, to express thanks to some whohavecontributed vitally in more recent years. Ourforemost appreciation is to the people of Rongelap and Utirik who have participated in the examinations, including the unexposed people comprising the control population. We treasure the friendship andtrust of these people. We are grateful to many Rongelap and Utirik peoplefor assisting the examining teamsoverthe years, including the Magistrates of both islands - at Rongelap: John Anjain, Billiet Edmond, Jabwe Jorju, and Niktimos Antak; at Utirik: Kabto Campus, Maja Lena, Harold, the school principal, and Joata, the health aide. Thesenior authoris most grateful to the many fine medical andotherspecialists (listed in Appendix 2) who haveso willingly given of their time and talents, without remuneration, to participate in the surveys. Without their dedicated efforts the surveys could never have succeeded. He is also greatly indebted to the manytechnicalassistants whohave contributed muchto the success of the surveys, particularly to Mr. W. Scott and Mr. D.