The results presented during the Third International ANCA Workshop, Washington, DC, 1990, allowed a better definition of the antigenic specificity of the antineutrophil cytoplasmic autoantibodies (ANCA). The large predominance of two major antigen specificities for proteinase 3 (PR3) and myeloperoxidase (MPO), in the group of vasculitic patients, was confirmed. PR3 and MPO are colocalized in the azurophilic granules of neutrophils and translocated to the cell surface during activation and thus are able to interact with ANCA after neutrophil preactivation. Furthermore, by comparison of amino acid and DNA sequences, the agreement was reached that PR3 was identical to AGP7, p29, and myeloblastin, described independently and involved in the control of growth and differentiation of leukemic cells. In addition to the two major ANCA antigens, a number of neutrophil cytoplasmic antigens recognized by ANCA have been previously identified (human leukocyte elastase [HLE], lactoferrin). It was established during the Third Workshop that these rare ANCA specificities, occurring in a limited number of patients, include a cationic antimicrobial protein (CAP57) and cathepsin G. However, the variety of ANCA antigen specificities contrasts with the fact that the vast majority of ANCA-positive sera are monospecific for a single ANCA antigen. Finally, the fine specificity of granulocyte-specific antinuclear antibodies (GS-ANA) occurring in rheumatoid arthritis and ulcerative colitis is still unknown, but clearly a substantial proportion of GS-ANA belongs to the ANCA family.