Various methods for the removal of leukocytes from whole blood have been compared and a new technique has been devised. This procedure consists of passing whole blood through a bed composed of microcrystalline cellulose and alpha-cellulose. The method is rapid, reliable, removes over 99.75 per cent of the leukocytes from blood, and does not seem selectively to retain reticulocytes or to release a significant proportion of leukocyte enzymes. Most of the platelets are also removed from anticoagulated blood, and platelet-free red cells can be obtained by passing defibrinated blood over the microcrystalline cellulose-alpha-cellulose bed.