he because a granulopenia and thrombopenia was developing concomitantly. However, the incidence and severity of infectious processes in all of the dose groups, in the non-exposed Marshallese and in the American medical team was identical. A few individuals were given mtibiotics at this time, but antibiotics were not used more freely than many physicians would have used them in a non-exposed population. The decision not to use prophylactic antibiotics was based on the fact that the dose of radiation was known with fair accuracy and it was believed to be sublethal. However, as granulocytes reached 1000/tam? and some were as low as 700/ram, some concern was felt about when and if prophylactic antibiotics should be used. However, all physicians present agreed that prophylactic antibiotics should not be instituted in these individuals because: 1. All were under continuous medical observation so that infection could be detected at onset. 2. Premature use of antibiotics might obscure indications for treatment and permit development of drug-resistant organisms in granulopenic individuals before antibiosis was needed. 3. There is no really accurate knowledge of level of granulocytes in man when infections develop and antibiotics might be needed, Although some of the individuals had severe febrile respiratory infections of unknown etiology, they were able to resist the infections, despite their depressed hemopoiesis, as well as normal individuals. a rather marked thrombopenia developed in all individuals from Rongelap and Ailinginae. Eleven had counts from 35,000 ~ 65,000 and all were below 150,000 at some time.