We have previously described circulating autoantibodies to a portal tract antigen in patients with primary sclerosing cholangitis. In this study the antigen has been shown by double-labelling studies to be specifically located in the nuclei of tissue neutrophils. Using isolated peripheral blood neutrophils and an immunoperoxidase technique, anti-neutrophil nuclear antibody (ANNA) was found in the serum of 84% of patients with primary sclerosing cholangitis (PSC: n = 32) with a median titre of 1/1000 and a peak titre of 1/500,000. ANNA was also detected in 86% of patients with inflammatory bowel disease alone (IBD: n = 76) with a median titre of 1/10 and a peak titre of 1/10,000. In contrast, only 12% of controls had ANNA, and in none was the titre greater than 1/10. In PSC the ANNA titre correlated with the serum aspartate transaminase concentration, suggesting that it is related to disease activity. In IBD the titre of ANNA was significantly higher in patients with recently active disease. There was no significant difference between the titres seen in ulcerative colitis and Crohn's disease. ANNA was not associated with neutropaenia. The results provide further evidence of involvement of autoimmune mechanisms in inflammatory bowel disease and primary sclerosing cholangitis.