Autotransfusion of 3H-cytidine labeled blood lymphocytes was performed in 4 normal subjects, 3 patients with non-leukemic malignant lymphoma (1 reticulum cell sarcoma, 2 lymphosarcoma), 2 treated, non-leukemic patients with chronic lymphocytic leukemia (CLL) and 11 untreated CLL patients. Immediately after autotransfusion on the average only 41.3% and 47.5% of the infused labeled lymphocytes were recovered in the blood of the normal subjects and of the untreated CLL patients, respectively. During the first hour, in the normal subjects a higher proportion of labeled cells disappeared from the blood that in untreated CLL patients. Thereafter, this initial rapid decrease ceased and levelled off into a plateau with rather constant recovery values. At this time (1-4 hours after autotransfusion), on the average only 6.7% of the normal lymphocytes, but 27.8% of the untreated CLL lymphocytes were recovered in the blood. In the non-leukemic lymphoma of the untreated CLL lymphocytes were recovered in the blood. In the non-leukemic lymphoma patients and treated CLL patients the autotransfused lymphocytes exhibited circulation kinetics similar to those of the normal lymphocytes. The majority of blood lymphocytes from untreated patients with CLL seem to be characterized by a poor exchange rate between intra- and extravascular lymphocyte pools and a prolonged intra-vascular life span. These findings agree with the impaired recirculation kinetics of CLL lymphocytes and their abnormal 0ehaviour in several "in vitro" tests dealing with other lymphocyte functions.