Inflammation and necrosis of blood vessel wall occurs in a dozen or so primary vasculitic disorders. An attempt to classify these diverse forms of vasculitis resulted in the Chapel Hill international consensus definitions, which used the vessel size as the determinant of classification (1). Wegener granuloma- tosis, microscopic polyangiitis, and Churg Strauss syndrome are described as small-vessel vasculitides and are acknowl- edged to be commonly associated with antineutrophil cyto- plasm antibodies (ANCA). These diseases share a common pathology with focal necrotizing lesions, which affect many different vessels and organs; in the lungs, a capillaritis may cause alveolar hemorrhage; within the glomerulus of the kid- ney, a crescentic glomerulonephritis may cause acute renal failure; in the dermis, a purpuric rash or vasculitic ulceration may occur. Wegener granulomatosis and Churg Strauss syn- drome have additional granulomatous lesions (for further re- view, see reference 2). The incidence of these diseases is increasing, with more than 20 per million affected and occur- ring more often in an elderly population (peak age, 55 to 70 yr) (3).