1. Three chimpanzees were given 900 r of whole body radiation followed by transfusion of homologous bone marrow. One animal survived for nearly six months.
2. Five chimpanzees were given 1200 r of whole body radiation; three of them were given homologous bone marrow. There was no difference in survival time of treated animals and of controls.
3. Observations were made on clinical, hematologic, bacteriologic and pathologic aspects of acute radiation injury.
4. There was no evidence of a "take" of the homologous marrow. The significance of the findings is discussed.