A safe and simple technique for the collection of large numbers of granulocytes from normal donors, based on the reversible adhesion of granulocytes to nylon wool filters, is described. The procedure is well tolerated by donors, and the granulocytes obtained show nearly normal bactericidal and phagocytic capacity in vitro. However, a surprisingly small median 1-hr posttransfusion increment of 233/cu mm was observed in leukopenic recipients lacking preformed leukocyte antibodies, as compared to the median increment of 850/cu mm reported following transfusion of leukocytes obtained by differential centrifugation. The safety and effectiveness of these granulocytes for the treatment or prevention of bacterial infections in granulocytopenic patients remains to be proven, however our initial experience with such transfusions has been encouraging.