ABSTRACT Following the detonation of a thermonuclear device in the Marshall Islands in the Spring of 1954 a significant amount of radioactive fallout material was deposited on neighboring Pacific islands. Of the 239 Marshallese people and 28 Americans exposed,64 Marshallese on the island of Rongelap received the highest dose of whole-body penetrating radiation (an estimated 175 r), the most extensive epilation and beta lesions of the skin, and small amounts of in- ternal absorption of radioactive materials. Other island groups were less heavily irradiated. This report is concerned with the epilation and beta lesions which occurred. Many individuals in the higher exposure groups complained of burning and itching skin during the first 24 to 48 hours after exposure. Epilation and skin lesions were beginning approximately two to three weeks after exposure, on skin areas contaminated fallout. Bluish-brown pigmentation of the fingernails was also a common finding. No of the observed, with primary or secondary erythema was observed and consistently the first evidence of skin damage was increased pigmentation in the form of dark brown to black macules, papules, and raised plaques. The lesions developed largely on the exposed parts of the body not protected by clothing, and occurred usually in the following order; scalp (with epilation), neck, axillae, antecubital fossae, feet, limbs, and trunk. Epilation and lesions of the scalp, neck, and foot (dorsal surface) were the most cammon. The majority of lesions were superficial without vesicle for- mation, and after simple dry desquamation healed and repigmented. Approximately 20 percent of the people in the highest exposure group developed deeper lesions, usually. occurring on the feet or neck and were characterized by wet desquamation with ulceration, ‘Mild burning, itching, and pain accompanied the lesions. The majority healed rapidly with nonspecific therapy. Re- sidual pigment aberration consisting of hyperpigmentation and lack of repigmentation and mild atrophic changes were noted in some deeper healed lesions at six months and one year. Regrowth of hair, normal in color and texture, began about nine weeks post-exposure and was complete at six months. Biopsies of typical lesions at three to six weeks showed changes consistent with radiation damage with marked epidermal damage and much less severe dermal damage. Biopsies at six months showed only a few residual changes. The nail discoloration had “grown out” com pletely at six months in all but a few individuals. Submitted by authors 16 February 1955. _ Issued by The Naval Medical Research Institute For Official Use — m3 --o! ot ca on 424