1. Normnal and irradiated rats underwent periods of cross-circulation with Shay granulocytic chloroleukemic rats.
2. The leukemic white blood cells disappeared rapidly from the arterial blood of the irradiated rat at a rate approximately identical with that of the removal of cross-transfused normal leukocytes.
3. Many leukemic cells remained in the arterial blood of normal recipent rats during the 90 miniute observation time after cross-circulation.
4. It was postulated that leukocytes transfused its rats by this method remain viable. In the irradiated leukopenic recipient, the rapid arterial blood removal rate of transfused cells may represent distribution in a depleted total body leukocyte "pool." Similarly, distribution may occur more slowly in normal animals with normally saturated tissue stores of leukocytes.
5. There was no indication that a large dose of total body irradiation increased the capacity of the reticulo-endothelial system to remove transfused leukocytes from circulation.