65 hypothyroidism in the two most growth-retarded boys with subsequent growth response to thyroid hormone treatment. Thyroid function tests in cases with thyroid abnormalities also indicated reduced thyroid function in some other children. Preliminary indications are that thyroid hormone treatmentinstituted in the exposed population in September 1965 is having a beneficialeffectin reducing thyroid nodules and stimulating growth of children. The importance of these thyroid developments in the Marshallese is discussed. OTHER STUDIES Hematological studies show that the leukocyte and Nal (TI) crystal in a portable shadow-shield type of counter. The Rongelap residents exposed in 1954 and the unexposed residents were indistinguishable by this method, both groups showing elevated '?*Cs body burdens of 10 to 20 nCi, kg body weight, or slightly less than 1 Ci total body burden and about “ooo this much for °°Co body burdens. These levels are about the same as or slightly lower than those reported previouslyfor the 1961 survey. Urine specimens werealso analyzed radiochemically for °’Sr and '°'Cs. The “Sr levels remain nearly the same as those found in 1961. In a comparison of the **’Cs excretion rate with the body burdens, a mean fractional] excretion rate of 0.00553/day was found. platelet levels of the peripheral blood of the ex- posed Rongelap people seem to have recovered to levels equal to those of the unexposed population. The blood levels of the Utirik population showed no obvious abnormalities and weresimilar to those previously noted. Chromosome studies of white cells of 51 peripheral blood cultures showed a lowincidence of 2-hit aberrations in the exposed people which was quite significant in view of the absence of any such aberrations in the comparison population. Blood volume andred blood cell volume studies showed that people of Rongelap have significantly reduced levels as compared with Americans. Cau- Acknowledgments The cooperation of many agencies and persons was necessary to carry out these surveys successfully. The authors are deeply grateful for valuable assistance to manyindividuals too numerous to name. Weareparticularly grateful to the people of Rongelap and Utirik Atolls for their cooperation in these examinations. Manyofficials of the Atomic Energy Commission, particularly Dr. Charles L. Dunham and Dr Aging studies have been repeated with the addi- H.D. Brunerandtheirstaff of the Division ofBiology and Medicine, and Mr. W.A.Bonnetand Mr. Neil Rassmussen of the Honolulu Operations Of- light extinction test, body potassium levels, and ments and in supporting the surveys in every wav statistical analysis. Curves of response for each aging parameter and an over-all biological age score curve are presented. Nosignificant increase in aging effects in the exposed population compared with the unexposed population could be de- Wearegratefulto the officials of the Department of the Interior, particularly Mrs. Ruth Van Cleeve and the officials of the Trust Territors of the Pacific Islands, including High Commussioners Mr. W.M. Goding and Mr. W.R. Noor- casiansliving in the Marshall Islands did not generally show this phenomenon. tion of several new parameters (vibratory sense, blood serum cholesterol) and with more refined tected. The over-all correlation of the biological age scores with chronological age was good. It was concluded that the tests employed may not have been sensitive enough to detect subtle effects of aging at this exposurelevel. ESTIMATION OF INTERNAL BODY BURDENS OF RADIONUCLIDES In the 1965 survey whole-body counting was done on 179 people with an 11'4-in.-diameter fice, were most helpful in coordination of arrangepossible. wood; the Acting Director of Medical Services, Dr. L.A. Howe; the District Administrator for the Marshall Islands, Mr. Dwight Heine, and his .\s- sistant, Mr. Danny Akimoto; the Director ofthe Majuro Hospital, Dr. John Iaman, and members of his staff; the Trust Territory Representative at Kwajalein, Mr. R. McKay, and Dr. Ezra Riklon at the Ebeye Hospital; all were most helpful. The Pacific Missile Range Facility at Kwajalein wasof great assistance in furnishing necessaryair- lifts and materials. Mr. Frank Granich and others