Prior to x irradiation, some 84 mice, similar to 45 used for the experiment, were given full blood analyses. The composite of 129 control mice gave the base line of normal blood evaluations for comparison with the blood averages of x-irradiated mice. The normal variations between the young virgins, mature, and the old females, were not agespecific and fell within the normal ranges. Multinucleate lymphocytes were found in 84.5% of all unirradiated mice of the three ages studied. Exposure of mice of different ages to 300 r of x rays caused permanent average depression of the platelets of all mice and of the hemoglobin and RBC of the old mice, and slight average depression of the RBC, but not of the hemoglobin, of the mature mice. Complete recovery from x irradiation insult was seen in the RBC and hemoglobin of the young, and in the hemoglobin oaly of the mature mice. By all tests the old mice showed the poorest recovery, and in RBC, platelets, and hemoglobin they showed permanent and severe average depression. The cytoplasmic inclusions, which have never been seen in blood of unirradiated control mice, appear to be nuclear fragments, and their appearance and occurrence may bemore » diagnostic of x irradiation insult. (73 references) (auth)« less