This diary appeared originally and rightfully in The Yale Journal of Biology and Medicine in 1965 and it covers the four months in 1945 Dr. Liebow, a pathologist and historian for the Yale Unit, spent with the Joint Commission for the Investigation of the Medical Effects of the Atomic Bomb in Japan. Their purpose was to analyze casualties, collect data and materials, determine the factors of distance and protection and prepare this study. Dr. Liebow spent about two of the four months on Hiroshima (almost an equal half of the personnel were assigned to Nagasaki) where only 3 of the 45 hospitals had been left standing. The few words describing the group's arrival there are decisively eloquent -- ""devastated, cold -- an ash"" but for the most part this is purely a record of the day by day acquisition of findings on more than 6000 casualties (bone marrow in exchange for vitamin pills) and the photo studies made (many of them will be reproduced here). Occasional ""pleasant interludes"" -- a trip here, a dinner there and testimonials to the participating Japanese doctors are interwoven with the purely clinical record, and in particular Dr. Liebow's warm regard for Col. Oughterson, the American behind the program, and the quiet, saddened Dr. Ishii. Judgment on the use of the bomb is not only implicit throughout but toward the close explicit. . . . A valuable residual.