In recent years there has been a great deal of effort expended in attempts to determine the "life span" of white blood cells. With the development of isotopic labeling techniques it was felt by many that finally real progress was being made and that definite figures could be given for the survival time of lymphocytes and granulocytes. Accordingly, most authorities now accept 9 to 13 days as the life span of the granulocyte1,2 and perhaps 200 days for the lymphocyte.3
However, to accept 200 days as the life span of the lymphocyte, one must reconcile this with a large background of sound experimental work extending back more than 30 years, which indicates that circulating mass of lymphocytes turns over very rapidly, implying a short life span.
These earlier conclusions were based on two main observations: (1) the comparatively huge numbers of lymphocytes entering the vascular tree via the