Graphs are presented showing hematologic data for persons exposed to ionizing radiation. These graphs were previously classified, but were requested to be used as part of a symposium on March 31, 1947, for a presentation on the protection of laboratory personnel handling radioactive materials. The presentation included discussions of tolerance dose for ionizing radiation, methods of calculating radiation dose from radioactive materials taken into the body, and methods used to diagnose early radiation damage. The graphs and charts contained in the present document show counts for platelets, reticulocytes, hemoglobin, red blood cells, lymphocytes with granules, white blood cells, granulocytes, and lymphocytes and monocytes for individuals exposed to ionizing radiation. Also included is data obtained on neutral red bodies in lymphocytes for unexposed persons and those exposed to chronic external radiation, chronic exposure to an unspecified material, and acute external exposure. Additional data is provided on percent of lymphocytes in differential count, absolute number of abnormal lymphocytes, total white blood count, percent of abnormal lymphocytes, and total lymphocyte count in unexposed subjects and persons exposed to gamma rays, alpha emitters, and uranium. Changes in refractile neutral red bodies in lymphocytes after acute radiation exposure are also shown.