Granulocytes were harvested from hematologically normal individuals using continuous flow centrifugation (CFC) or filtration leukapheresis (FL). The isolated granulocytes were labeled in vitro by 3H-diisopropyl fluorophosphate (3H-DFP) and autotransfused. Their intravascular fate was analyzed by autoradiography. Immediately after autotransfusion the majority of granulocytes administered, collected in the marginal granulocyte pool. Margination was particularly prominent in granulocytes isolated by FL. The distribution of transfused granulocytes between the circulating and the marginal granulocyte pool showed wide and irregular fluctuations in time. Margination of transfused granulocytes was counterbalanced, and its fluctuation between the two intravascular pools was stabilized by prednisone treatment. The transit of transfused granulocytes from blood to tissue seemed to be governed by a random process, the half-disappearance time being either normal or prolonged. Compatible granulocytes administered to hematologically normal recipients circulated for at least 20 h.