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 someotherchildren. 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 platelet levels of the peripheral blood of the exposed Rongelap people seem to have recovered to levels equalto those of the unexposed population. The blood levels of the Utirik population showed no obvious abnormalities and were similar to those previously noted. Chromosomestudies of white cells of 51 peripheral bleod cultures showed a low incidence of 2-hit aberrationsin the exposed people which was quite significantin view of the absence of any such aberrations in the comparison population. Blood volume andredblood cell volume studies showed that people of Rongelap havesignificantly reduced levels as compared with Americans, Cau- casiansliving in the Marshall Islands did not generally show this phenomenon. Aging studtes have been repeated with the addition of several new parameters (vibratory sense, light extinction test, body potassium levels, and blood serum cholesterol) and with morerefined statistical analysis. Curves of response for each aging parameter andan over-all biological age score curve are presented. Nosignificant increase in aging effects in the exposed population compared with the unexposed population could be detected. 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%-in.-diameter Nal (T1) crystal in a portable shadow-shield type of counter. The Rongelap residents exposed in 1954 and the unexposed residents wereindistinguishable by this method, both groups showing elevated '*’Cs body burdensof 10 to 20 nCi/kg body weight, or slightly less than 1 wCi total body burden and about Moco this much for °°Co body burdens. These levels are about the same as or slightly lower than those reported previously for the 1961 survey. Urine specimenswerealso analyzed radiochemically for °°Sr and '*7Cs, 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 meanfractional excre- tion rate of 0.00553/day was found. Acknowledgments The cooperation of many agencies and persons was necessary to carry out these surveys success- fully. The authors are deeply grateful for valuable assistance to manyindividuals too numerousto name. Weare particularly grateful to the people of Rongelap and Utirik Atolls for their cooperation in these examinations. Manyofficials of the Atomic Energy Commis- sion, particularly Dr. Charles L. Dunham andDr. H.D. Brunerandtheirstaff of the Division of Biol- ogy and Medicine, and Mr. W.A. Bonnet and Mr. Neil Rassmussen of the Honolulu Operations Office, were most helpful in coordination of arrange- ments and in supporting the surveys in every way possible. Wearegrateful to the officials of the Depart- ment of the Interior, particularly Mrs. Ruth Van Cleeve and the officials of the Trust Territory of the Pacific Islands, including High Commissioners Mr. W.M. Goding and Mr. W.R. Noor- wood; the Acting Director of Medical Services, Dr. L.A. Howe; the District Administrator for the Marshall Islands, Mr. Dwight Heine, and his As- sistant, Mr. Danny Akimoto; the Director of the 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 wasofgreatassistance in furnishing necessaryairlifts and materials. Mr. Frank Granich and others