The demonstration of autoantibodies to different myeloid lysozomal enzymes has opened a new area for the study of vasculitic syndromes. Autoantibodies producing a granular cytoplasmic staining by IIF (c-ANCA, probably directed to a putative serine protease) are closely associated with Wegener's granulomatosis. Autoantibodies to myeloperoxydase (producing a perinuclear staining by IIF, p-ANCA) are associated with idiopathic crescentic glomerulonephritis and polyarteriitis nodosa/Churg Strauss syndrome. These strong associations suggest a pathophysiological role for the autoantibodies in the diseases with which they are associated.