The target autoantigen associated with cANCA was identified in 1990 as proteinase 3 (PR-3) (112), a 29kD neutrophil serine protease of azurophil granules, previously characterized by Kao (113). Confirmation of PR-3 as the major autoantigen in Wegener's granulomatosis was attested by other workers (114, 115). The presence of cANCA denotes a spectrum of disease varying from idiopathic pauci-immune necrotising glomerulonephritis to extended Wegener's granulomatosis. In extended Wegener's granulomatosis, characterized by granulomatomous inflammation of the respiratory tract, systemic vasculitis and necrotising crescentic glomerulanephritis, cANCA is present in greater than 90% of patients (116, 117). Nevertheless, it should be stressed that clinical observations of the last years suggest that the test for ANCA may not be as specific for Wegener's granulomatosis as previously thought (118). In the so-calIed limited Wegener's granulomatosis without renal involvement, cANCA is detected in 67-86% of patients and in 40-50% of patients with pauci-immune necrotising glomerulonephritis (119). However, not all cANCA positive serum react with PR-3 antigen. Reported sensitivity of anti-PR-3 antibodies in cANCA positive serum lies between 70% to 100% (119-121). A recent report suggests that cANCA positive serum may contain antibodies against antigens other than PR-3 (119) but as yet the role of these antibodies is unclear. Prognostically, rises in antibody titer are thought to predict relapse and to help to differentiate relapse from opportunistic infection (122-125), although some recent evidence suggests that, in a minority of patients, cANCA/anti-PR-3 titers do not follow disease activity (126).