Antineutrophil cytoplasmatic autoantibodies (ANCA) have been tested in this laboratory for more than two years with a 3-fold increase in tests and positive results. The initial association with Wegener's granulomatosis has since been extended to microscopic polyarteritis and rapidly progressive glomerulonephritis. We review the published data. ANCA are not simply another laboratory test but have become an important tool for diagnosis, treatment monitoring and prevention of relapses in many vasculitis syndromes including some forms of rapidly progressive glomerulonephritis. The ANCA-associated antigens have been identified as a serin-proteinase and myeloperoxidase. This provides insights into the pathogenesis of the ANCA-related diseases.