Fukuryu Maru 5, with 23 crew members, was exposed 80 miles east of Bikini (see Appendix VI). After extensive decontamination procedures, exposed individuals were ob- served closely for two months (and at frequent intervals thereafter) by spe- cial medical teams assembled at the Kwajalein Naval Base, then were resettled in other islands of the Marshalls group. Medical problems that arose were treated on an individual basis as clinically indicated. C. Early Clinical Effects A more detailed summarization of symptoms and clinical findings in the immediate postexposure period is contained in the 20-year report (1). Nausea occurred within 48 hours in two-thirds of those on Rongelap, the most heavily exposed group, with vomiting and diarrhea in 10%. By contrast, none of those on Utirik (the least exposed group) and only 5% of those on Ailingnae (with intermediate expesur2s) experienced nausea. About cne-fourth of those on Rongelap and Ailingnae complained of skin irritation and itching; about one-fourth of this group also had eye irritation. These symptoms were quite probably radiation-induced, mostly by direct exposure to high-energy beta emitters, since most of the affected subjects later developed epilation and a few developed conjunctivitis. Some of these syuptoms may have been aggravated by the caustic effects of the highly alkaline calcium oxides produced by fireball vaporization of the coral island. Dermal effects were most pronounced on the scalp, neck, dorsa of the feet, axillae, and antecubital tossae. The severity of skin lesions in each group of people appeared to be proportional to the amount of fallout material observed on their atoll. On Rongelap, fallout was described as similar to snowfall, and it actually whitened the hair and adhered to the skin. Partial epilation began within two weeks and eventually affected half of this group. A less dense, powdery mist fell on Ailingnae and Rongerik, and dermal effects there were less evident, epilation beginning in three weeks and affecting <202 of the people. On Utirik, the fallout debris was not visible, and no skin lesions or epilation developed. Since peripheral blood changes are among the most sensitive and reliable clinical indicators of radiation damage, these were studied closely. Significant hemogram alterations soon became apparent among the more heavily exposed subjects, both on an individual basis and in comparison with mean values for nonexposed Marsh2zllese controls grouped according to sex and five-year age intervals (see Section III). In the Rongelap population, absolute neutrophil counts in all age groups fell 20 to 30% during the second postexposure week and 50% by the fifth week, gradually returning to normal after one year. Lyaphocyte counts dropped rapidly to abcut one-half adult contr.1 values by the third day. By two years they were nearly normal. Maximum lymphocyte depressions were even greater (25% of control means) in the younger age groups, who generally exhibited more profound hematologic effects than the adults. Platelet counts reached a low of about one-third control levels during the fourth post-exposure week and eventually required more than two years to return to normal. No significant changes occurred in hematocrit or red blood cell counts.