Distribution of FITC⁺ blood lymphocytes and CM-DiI⁺ lymph lymphocytes in the blood and lymph compartments. Top panel; in this and all seven experiments performed, the concentration of blood lymphocytes remained consistently higher in blood (▪) than in lymph (○). Middle panel; in contrast, lymph lymphocytes rapidly disappeared from the blood and reached a higher concentration in lymph from about 1 day onward. Bottom panel; to rule out the possibility that the blood labeling protocol hindered lymphocyte recirculation, in one experiment the leukocytes were depleted from a blood sample and replaced with lymph lymphocytes, then the blood was labeled with FITC and reinfused as usual. The lymph lymphocytes reached a higher concentration in lymph than in blood; therefore the blood labeling protocol does not appear to affect the ability of lymphocytes to leave the blood and enter lymph.