20 patients with biopsy-proven Wegener's granulomatosis (WG) and 95 control patients underwent determination of anticytoplasmic antibodies (ACPA) by the indirect immunofluorescence technique to assess the specificity and sensitivity of ACPA for WG. Of 14 untreated patients with WG, 13 were ACPA-positive. All these patients became ACPA-negative under immunosuppressive treatment. 4 patients treated with immunosuppressive drugs and 2 patients in remission after termination of therapy had a negative ACPA-test. ACPA were detected in 9 patients of the control group (two patients with Henoch Schoenlein purpura, two patients with systemic vasculitis, 2 patients with systemic diseases, and 1 patient with systemic lupus erythematodes). With that we achieved a specificity of 90.5% and a sensitivity 65.0%. In conclusion the ACPA-determination is very helpful for diagnosis and follow-up of WG.