A high frequency of a variety of autoantibodies has been found in sera from patients with primary sclerosing cholangitis (PSC). The prevalence of all types of autoantibodies in PSC was significantly higher than that in healthy controls and patients with isolated inflammatory bowel disease. The titres of the antibodies were rather elevated, particularly in females, and most of them were IgM. The most frequent type of antinuclear antibody was the 'homogenous' type, which is a marker of many autoimmune diseases. The overall prevalence of the antibody was 35%, whereas in female patients it reached 67%. No correlation was found between autoantibody positivity and any clinical parameter. The present findings support the hypothesis that immunological factors may be relevant in PSC.