1. Introduction.- 2. Methods of Leukodepletion.- 3. Enumeration of Low White Cells.- 4. Mechanisms of Leukodepletion by Filtration.- 5. Role of Contaminating White Blood Cells in the Storage Lesions of Red Cells and Platelets.- 6. Leukodepletion to Prevent Transfusion Reactions: Effects on Cytokines and Other Biologic Response Modifiers.- 7. Leukodepletion and Alloimmunization.- 8. Role of Donor Leukocytes and Leukodepletion in Transfusion-Associated Viral Infections.- 9. Leukocyte Depletion and Transfusion-Induced Immunomodulation.- 10. The Role of Leukocyte Depletion in Prevention of Transfusion-Related Acute Lung Injury.- 11. The Role of Leukocyte Depletion in the Prevention of Reperfusion Injury Associated with Open Heart Surgery.- 12. The Use of Leukodepleted Blood Components for Neonates and Infants.- 13. Leukocyte Depleted Blood Transfusion in Hematopoietic Stem Cell Reconstitution Therapy.- 14. Cost-Effectiveness of Leukodepletion.