Before the mid-1980s the only autoantibody widely used to assist in diagnosing vasculitic disease was IgG antibody to the α₃ domain of the noncollagenous part of type IV collagen (anti-glomerular basement membrane). Since that time, antineutrophil cytoplasmic antibodies (ANCAs) directed at the azurophilic granule proteins proteinase-3 and myeloperoxidase have been established as clinically useful autoantibodies to support a diagnosis of Wegener's granulomatosis, microscopic polyangiitis, Churg–Strauss syndrome and limited forms of these primary, small vessel necrotizing and often granulomatous vasculitides. The establishment of standardized methods for identifying those antibodies was needed before they could be used in clinical practice. The levels of both types of ANCAs tend to increase in parallel with the degree of clinical disease activity, and they decrease with successful immunosuppressive therapy. More than one assay may have to be used to discover imminent exacerbations in proteinase-3-ANCA associated syndromes. Although autoantibodies to endothelial cells may be important players in the pathogenesis of several vasculitic conditions, they have not gained clinical popularity because of lack of standardized detection methods.