Introduction On Maron 1, 1954, an experimental thermonuclear device was exploded at the U. S. Atomic Energy Commission’s Eniwetok Proving Grounds in 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 injurious radiation levels; therefore, evacuation was ordered, and was carried out as quickly as possible with the facilities available to the Task Force. Although the calculated accumulated doses to the exposed human beings were believed to be well below levels that would produce serious injury or any mortality, the Commanderof the Task Force requested the Department of Defense and the U. 8S. 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. Responsibility for organization of the medical team was shared by the Armed Forces Special Weapons Project, Department of Defense, and the Division of Biology and Medicine, U.S. Atomic Energy Commission. Experienced professional and technical personnel were immediately available from the Naval Medical Research Institute and the U.S. Naval Radiological Defense Laboratory. Since speed was essential in the organization and transport of the medical team to the mid-Pacific area, the assistance of the Medical Department of the Navy was requested, and was promptly received from the Surgeon General, A team was organized from personnel of the two Navy laboratories and representatives of the AEC Division of Biology and Medicine and the Interim care and study had} been capably handled by the small medical debartment of the U. S. Naval Station,. Kwajaleif, Marshall Islands The commanderof the ngval station had arranged living facilities for the exposed Marshallese, and installed laboratdry and clinical facilities as requested immediatdly upon arrival of the medical team. Full cooperation and support from all agencies in the field enabled the ngedical team to operate at maximum efficiency,|so that the degree of radiation injury cougd be assessed the immediate effects without Nevertheless it is planned t@ evaluate the medical and genetic status of the group at appropriate intervals with a vi#w to learning what if any of the known late #ffects of radiation exposure may be observed. Obviously and indeed fortunately the numbey of persons receiving 75 roentgens exposurefand greater is too small to make it possible tofdetermine with any degree of accuracy the effget on life span. In addition to providing mpdical care for these persons, the team accungulated a large body of scientific observations gn radiation injury in human beings. The ifitial data have been supplemented byfield resifrveys 6, and 24 months after the original invéstigation. The results of this work areJsummarized in the present volume. The datafwhich were obtained substantially increase the fundamental knowledgeof radiation injury Ind the medical capability of caring for perspns exposed to large doses of radiation. Armed Forces Special Weapons Project. The team was air lifted to the Marshall Islands, arriving on the eighth day after the explosion. til