Neutrophil antigens may be classified into two major categories: antigens shared with other cells and antigens specific for neutrophils. The first category includes the ABH, I, i, 5a,b and HLA determinants. Additional antigens with special characteristics in this category are the blood-group U, Kx, JkaJkb, and Ge determinants which apparently neutrophils share only with erythrocytes. Neutrophil-specific antigens include the NA1, NA2, NB1 and 9a. These specificities are detected by the agglutination test and have been shown to be present on mature neutrophils. Independent allospecificities, detectable by the granulocytotoxicity test, may also exist. In addition, neutrophil antigens, which are species-specific, have been identified by the use of xenogeneic antibodies. The EDTA-dependent agglutination test remains a most reliable assay for the study of neutrophil-specific antigens. The lack of reproducibility known in the leukoagglutination reaction does not pertain to the modification used in the assay of neutrophil-specific antibodies. It does apply, however, to those tests that were performed in the absence of EDTA, and in connection to the study of HLA-related antigens. For every pathophysiological state involving the erythrocyte antigens a neutrophil analogue is observed, the difference being in symptomatology which is related to the structural and functional characteristics of the cells: febrile and pulmonary transfusion reactions result from incompatibility neutrophils. It is found that similarity in the HLA antigens and nonreactivity in the MLC test do not preclude immunization against neutrophil-specific antigens. Therefore, it is probable that febrile and pulmonary reactions will occur in the recipients of multiple granulocyte transfusions, even though donors and recipients may be considered "histocompatible" by the HLA assays. It has been shown that fetal-maternal incompatibility can cause neonatal neutropenia, and several forms of autoimmune neutropenia are described: in "idiopathic" neutropenia of infancy, autoantibodies have been found to have specificity against NA1 and NA2 and in one adult, autoimmune neutropenia due to anti-NA1 antibody has been observed. Neutropenia also occurs due to idiopathic, cold-reacting antileukocyte antibodies, and with cold agglutinins associated with lymphoma, infectious mononucleosis, and Mycoplasma pneumonia. Although the role of neutrophil antigens in bone marrow transplantation has not as yet been determined, these antigens are undoubtedly immunogenic and potentially play an important role in neutrophil compatibility. It is obvious that neutrophils cannot survive in the presence of antineutrophil antibodies.(ABSTRACT TRUNCATED AT 400 WORDS)