Two thousand nine hundred twenty-seven granulocyte collections were made using continuous-flow centrifugation with the Aminco Celltrifuge I, the Fenwal Celltrifuge II, and the IBM 2997. There were 231 recipients and 246 donors. In 32 patients attempts to provide daily granulocyte transfusions from a single donor were unsuccessful owing to clotting of the silastic-Teflon arteriovenous shunt. Repeated granulocyte donations produced severe anemia requiring red cell transfusions in all the females and most of the males who had previously donated marrow for transplantation. Granulocyte collections were similar when collected with the Celltrifuge I or the IBM 2997, but collections with the Celltrifuge II were smaller. Infusion of hydroxyethyl starch directly into whole blood as it entered the centrifuge increased granulocyte collections. Granulocyte collections decreased with increasing number of daily collections.