Granulocyte antigens play an important role in cell function including adhesion, cell activation, and binding of immunoglobulins. The purpose of these studies is to better define the molecular basis of variations in neutrophil antigens and their role in neutrophil function. The role of antibodies specific for granulocyte antigens in transfusion reactions is also being investigated. During pregnancy or following transfusion people sometimes make antibodies directed to antigens expressed by granulocytes or neutrophils. When blood donors produce antibodies to neutrophil specific or HLA antigens the inadvertent transfusion of these antibodies has been associated with transfusion reactions. However, not all patients given blood products with neutrophil or HLA antibodies experience a transfusion reaction and the type of transfusion reaction varies among individuals. Studies are underway to investigate the role of antibodies directed to leukocytes in transfusion reactions.