Introduction On March 1, 1954, an experimental thermonuclear device was exploded at the U. S. Atomic Energy Commission’s Eniwetok Prov- ing Groundsin the Marshall Islands. Following the detonation, unexpected changes in the wind structure deposited radioactive materials on inhabited atolls and on ships of Joint Task Force 7, which was conducting the tests. Radiation surveys of the areas revealed radiation levels above permissible levels; therefore, evacuation was ordered, and was carried out as quickly as possible with the facilities available to the Joint Task Force. Although the calculated accumulated doses to these people were believed to be below levels that would produce serious injury or any mortality, the Commander of the Task Force requested the Department of Defense and the U. S. Atomic Energy Commission to organize a medical team to provide the best possible care of the exposed persons and to make a medical study of the exposures. The medical surveys of the Marshallese exposed to the fallout from the March 1, 1954 nuclear test detonation at the Eniwetok Proving Ground, have been published under the editorship of Dr. Victor P. Bond,” Dr. Eugene P. Cronkite," who headed the first two surveys, and Dr. Robert Conard,” who led the 2-year follow-up study. The present report brings together the radiological data developed by the Joint Task Force 7, Applied Fisheries Laboratory of the University of Washington, U. S. Naval Radiological Defense Laboratory, Health and Safety Laboratory, New York Operations Office of the Atomic Energy Commission, and the Office of Naval Research. This report was undertaken by Dr. Gordon M. Dunning at the request of the Atomic Energy Commission. Dr. Dunning at the time of the fallout was a representative of the Division of Biology and Medicine, Atomic Energy Commission to Joint Task Force 7 and participated in the early surveys and in the evacuation of the natives of Rongelap and Utirik Atolls to Kwajalein. It is hoped that this document will provide valuable information to those agencies and persons responsible for planning protection against radioactive fallout from whatever source. It not only gives a picture of the initial contamination, but in addition documents the radioactive decay as it has occurred on the Rongelap Atoll over a 2-year period and thus suggests the developing patterns of the transfer of radioactive materials from the soil and water into the food chain. Cuares L. Dunnam,M.D., Director Division of Biology and Medicine U. S. Atomic Energy Commission DOE ARCHIVES