There has been a profusion of studies related to the pathogenesis of antineutrophil cytoplasm antibody-associated small vessel vasculitis. Further definition of epitopes on the major antigens, proteinase-3 and myeloperoxidase, has been sought, and intracellular signal transduction pathways after antineutrophil cytoplasm antibody-neutrophil interactions are beginning to be explored. Antineutrophil cytoplasm antibody stimulation of neutrophils has highlighted the functional importance of the accelerated death that follows the initial activation. The consequences of neutrophil and monocyte activation for endothelium and tissue damage continue to point toward an inflammatory process that has become dysregulated. Factors that initiate vasculitis are being identified slowly. The most secure identifiable environmental trigger is the antithyroid drug propylthiouracil. It is likely that environmental factors operate against a background genetic susceptibility, and polymorphisms in genes for proteins associated with inflammation are being tested for possible links with small vessel vasculitides.