ANCA mainly recognize proteinase 3 (cytoplasmic fluorescence) in Wegener's granulomatosis and myeloperoxidase (perinuclear fluorescence) in other types of vasculitis. A causative role of ANCA seems not obvious because: a) active generalized Wegener's granulomatosis may exist with no detectable ANCA, b) ANCA titres don't reliably parallel clinical activity and c) of the increasing diversity of clinical situations where ANCA are described. Nevertheless, some lines of evidence point to a pathogenetic role of ANCA, especially in vascular lesions genesis: a) ANCA may prevent inactivation of antigenic proteases by antiproteases, b) translocation at the outer membrane of intracellular antigens make them accessible to ANCA, c) activation of polymorphonuclear leucocytes and increase of their aggregation and cytotoxicity to endothelial cells are specifically induced by ANCA, d) proteinase 3 and myeloperoxidase may adhere to the endothelial cell membrane and then be recognized by ANCA, e) a specific T-lymphocyte response to ANCA antigens could be elicited in Wegener's granulomatosis and f) an in vivo model of ANCA-related glomerulonephritis has recently been established.