The avg. lifespan of leukocytes has been estimated by following the incorporation of p32 into the desoxyribosenucleic acid of the cells. Using this method, the lifespan of the avg. leukocyte was estimated to be 13.2 days. The time the cells actually circulate in the blood stream was estimated to be 9.2 days, the difference representing time spent at the site of formation before release into the circulation.