Abstract To evaluate the diagnostic significance of neutrophil cytoplasmic antibodies in chronic liver diseases, we assessed the prevalence of neutrophil cytoplasmic antibodies in autoimmune liver diseases, in particular in primary sclerosing cholangitis, autoimmune chronic active hepatitis and primary biliary cirrhosis, and we also determined the specificity of perinuclear-pattern neutrophil cytoplasmic antibodies for these autoimmune liver diseases by testing sera from patients with nonautoimmune chronic liver diseases. Neutrophil cytoplasmic antibodies were detected in 79% of sera from patients with primary sclerosing cholangitis (n = 24), in 88% of sera from patients with autoimmune chronic active hepatitis (n = 24) and in 28% of sera from patients with primary biliary cirrhosis (n = 25). The presence of neutrophil cytoplasmic antibodies in these diseases correlated significantly ( p < 0.008) with the presence of cirrhosis. Neutrophil cytoplasmic antibodies were not detected in nonautoimmune liver diseases. All neutrophil cytoplasmic antibody-positive sera produced a perinuclear fluorescence pattern on ethanol-fixed granulocytes. On neutrophils fixed with paraformaldehyde, a granular cytoplasmic immunofluorescence pattern was observed, demonstrating the cytoplasmic nature of the antigen or antigens involved. Further characterization studies showed that neutrophil cytoplasmic antibodies in autoimmune liver diseases are not directed against myeloperoxidase, proteinase 3 or elastase, the neutrophil cytoplasmic antibody specificities associated with necrotizing vasculitis, glomerulonephritis or both. On Western blots neutrophil cytoplasmic antibodies in autoimmune liver diseases showed reactivity with either lactoferrin, a 67/66-kD protein combination or a 40-kD polypeptide. Reactivity with either of these proteins was observed in sera from patients with primary sclerosing cholangitis (38%), autoimmune chronic active hepatitis (17%) and primary biliary cirrhosis (20%). Because the same specificities have been found in neutrophil cytoplasmic antibody-positive sera from patients with inflammatory bowel disease and rheumatoid arthritis, these data suggest that these neutrophil cytoplasmic antibodies are a corollary of chronic inflammation.