2.1 Introduction Wuen Tue Exposep groups were first seen at Kwajalein after evacuation from their native atolls, the amount of radiation they had received was not known with certainty. It was known, however, from instrument readings taken at the sites of the fallout and from monitoring all individuals, that a significant amount of penetrating irradiation to the entire body had been received and that extensive contamination of the skin and possible internal deposition of radioactive materials had occurred. The nature of the irradiating material and the cir- cumstances of exposure prevented a precise evaluation of dosage (see introduction). Even if the precise dose had been known it would not have been possible to predict the biological effects since the quantitative response of man is not known. Accordingly, a complete medical history and physical examination was obtained on each individual and numerous follow-up examinations were carried out. In addition, routine sick-call was held twice daily and inspection of the skin of all individuals was made at. frequent intervals. Medical care was available at all times. Hospital facilities were available at the Kwajalein Naval Dispensary, and support by the more extensive medicalfacilities of the U. S. Pacific Fleet had been promised if needed.° From descriptions of the amount of fallout material and from radioactivity measurements, it was apparent that Group I (Rongelap) had received the highest doses of radiation, Group II (Ailinginae) and Group III (Americans) an intermediate amount and Group IV(Utirik) the least. From physical dosimetry it waslater estimated that Group I had received approximately 175 r of gamma radiation; Group II, 69 r; Group III, 78 r; and Group IV, 14 r. The most serious clinical and laboratory manifestations of irradiation appeared in Group I and II. The only abnormalities that could be attributed with certainty to irradiation were skin lesions, epilation, granulocytopenia and thrombocytopenia. The skin lesions were first observed between the 12th and 14th post-exposure days. These lesions were most prevalent in Groups I and II but were present to a slight extent in Group III. Details of the skin symptoms and lesions and their treatment are reported in Chapter 3. Details of hematologic studies are presented in Chapter IV. Granulocytopenia and thrombocytopenia of marked degree developed in manyindividuals of Groups I and II and wasof sufficient severity to warrant serious consideration of prophylactic and therapeutic measures for potential sequelae of these cellular deficiencies. In view of the conflicting opinions about the value of prophylactic and therapeutic measures such as antibiotics and whole blood transfusions in the treatment of radiation disease (1-5), it was decided that therapy would be instituted only as indicated clinically for specific conditions as they arose. In order to determine the effect of the internal deposition of radioactive material on the course of the externally induced radiation injury, it was necessary to determine the degree of internal radioactive contamination. Details of the measurement of internal deposition of radionuclides are considered in Chapter V. It is sufficient to state here that the contribution from the internally deposited radionuclides to the total acute dose was insignificant. 2.2 Symptoms and Signs Related to Radiation Injury Severna, Symproms Tuartdeveloped during the first two days could be attributed to radiation. These symptoms were associated with the skin and the gastrointestinaltract. Itching and burning of the skin occurred in 28 percent of Group I (Rongelap), 20 percent Crt 15 G6 UC92