According to the literature, autoantibodies against extranuclear components of polynuclear granulocytes (ACPA) are almost exclusively present in sera of patients with Wegener's granulomatosis and their serum concentrations reflect disease activity. When measurement of these autoantibodies was introduced in our routine laboratory, 12 out of the first 70 samples gave positive results by enzyme immunoassay and by indirect immunofluorescence on alcohol-fixed granulocytes. The 12 patients with ACPA proved to have Wegener's granulomatosis. The titers were distinctly higher in patients without therapy than in those under an immunosuppressive regimen. As a control, 250 sera were tested of patients with various disorders such as SLE, rheumatoid arthritis, acute and chronic hepatitis etc. ACPA were detected in 4 individuals (1 patient with acute non A/non B hepatitis, 2 patients with chronic aggressive hepatitis and 1 hemodialysis patient with unclear glomerulonephritis). These results further confirm the diagnostic value of ACPA in Wegener's granulomatosis.