The author carried out studies on radiated whole blood transfusion upon leukopenia in rabbits following total body irradiation with 300r X-ray. The following conclusions were obtained: 1. In first control group which were only exposed to X-irradiation, diminished leukocyte count appearde at the second day after radiation at first, about thirty nine percents and thirty five percents of base line level occurred at the 5th and 8th days after radiation respectively, thereafter recovery of leukocyte was begun, but not recovered to the base line level up to two months after radiation. 2. In second control group which were transfused upon leukopenia following X-irradiation with 30ml. of normal rabbit whole blood, there was no significant difference from first control group except marked increased leukocyte count at the next day of transfusion. 3. Transfusions of 30ml. of radiated rabbit whole blood with 300r X-ray upon leukopenia in rabits following irradiation with 300r X-ray were almost same results as second control group at the first three days after transfusion, but marked increased leukocyte count was occurred at the fourth days after transfusion, and preirradiated count was achieved at the tenth days after transfusion. Irradiated whole blood transfusion were shown to be capable to recover the leukopenia by radiation effectively.