Reprinted from Rapiration REseARCH Voiume 3, No. 2, October 1955 Academic Press [nc. Printed in U.S.A. 29. The Characteristics of Fallout Material and the Effects of Fallout Radiation on Human Beings, E. P. Cronzits, N. R. Sauuman, C. A. Sonpnaus, R. A. Searp, and V. P. Bonn, Naval Medical Research Institute, Bethesda, Maryland, and U. 8. Naval Radiological Defense Laboratory, San Francisco, California. Human beings were accidentally exposed to fallout radiation commencing approximately 5 hours after explosion of a large nuclear device. The fallout material was visible (snowlike). It contaminated skin, clothes, and surroundings, producing skin lesions, whole-body effects, and internal deposition of small amounts of radionuclides. Whole-body exposure occurred at nO a cettan te tee TE tee four levels: 175 r, 78 r, 69 r, and 14 r midline dose of radiation. Nausea and some vomiting occurred on the day of exposure in the two highest exposure groups. Marked depression of granulocytes and platelets occurred, but agranulocytic infections and hemorrhage did not occur. No prophylactic therapy was administered. It can be concluded that after these levels of exposure prophylactic therapy is not indicated.