A total of 67 leukaphereses were performed with the continuous flow centrifuge (CFC) on 27 healthy donors for the purpose of obtaining increased yields of granulocytes for infusion into septic patients with acute leukemia accompanied by severe granulocytopenia. The addition of hydroxyethyl starch (HES) to the input line of the CFC significantly (P < 0.005) increased the total number of leukocytes and/or granulocytes collected per donation. A mean yield of 9.72 x 109 and 4.65 x 109 total granulocytes were collected by the HES treated and control group donors, respectively. The efficiency of cell collection as evidenced by the total number of leukocytes and/or granulocytes harvested per liter of processed blood was also significantly (P < 0.005) improved by the addition of HES to the continuous flow centrifuge. Significant alterations in hematologic parameters were not experienced by HES treated donors undergoing initial and multiple procedures. Pre- and postdonation leukocyte and platelet counts, hemoglobin, prothrombin time, partial thrombosplastin time, and leukocyte differential counts were no different whether or not HES was employed for granulocyte collection. The results of the present study demonstrate that increased yields of granulocytes can be harvested by the addidion of HES to the continuous flow centrifuge and made available for supportive therapy to patients experiencing granulocytopenia induced by malignant disease or its treatment.