1. Lymphocytes in dogs have been labeled by means of the DNA-P32 incorporation technic.
2. In the thoracic duct, a high level of lymphocyte DNA-P32 specific activity is reached within two hours. After 24 to 30 hours, the activity falls to a lower level which is then maintained for at least 160 hours.
3. Lymphocyte-granulocyte separations on the blood revealed that DNA-P32 specific activity reached a peak on the fourth day for both lymphocytes and granulocytes.
4. These findings are consistent with a short maturation time for the lymphocyte and a short intravascular time.