Introduction The discovery of autoantibodies for erythrocytes in acquired hemolytic anemia (AHA)* and for platelets in idiopathic *The following abbreviations will be employed throughout this paper: PVP, polyvinylpyrrolidone; ITP, idiopathic thrombocytopenic purpura; DLE, disseminated lupus erythematosus; PMN, polymorphonuclear leukocyte; TEPA, triethylene phosphoramide; PTC, plasma thromboplastin component deficiency; PNH, paroxysmal nocturnal hemoglobinuria; AHA, acquired hemolytic anemia. thrombocytopenic purpura (ITP) led to a search for antibodies for leukocytes in leukopenic persons. The observation by Moeschlin and Wagner in 19521,2of the presence of a leukoagglutinin in the serum of a patient with granulocytopenia following aminopyrine (Pyramidon) administration introduced a series of publications demonstrating agglutinins for leukocytes in human sera and the antigens of leukocytes.3-23 The contributions of these studies were (1) the development of relatively simple techniques for the detection of leukoagglutinins, (2) a limited survey of disorders in which leukoagglutinins may be found, (3) a brief description of the