Serum antibody to carbonic anhydrase II (CA II) has been reported in patients with autoimmune pancreatitis and its related autoimmune liver diseases. To evaluate its diagnostic significance, we studied serum antibodies to CA II and also CA I in patients with chronic viral hepatitis by enzyme-linked immunosorbent assay and reviewed its prevalence previously reported in patients with liver diseases. Anti-CA II antibody was detected in 5 of 20 patients with chronic hepatitis type C (25%, p<0.05 versus normal controls), 2 of 10 patients with chronic hepatitis type B (20%, not significant versus normal controls), and 1 of 30 normal controls (3%). Anti-CA I antibody was detected in 3 of 20 patients with chronic hepatitis type C (15%, not significant versus normal controls). Anti-CA II antibody has previously been reported as being associated with a variety of liver diseases, including primary biliary cirrhosis with or without anti-mitochondrial antibody, autoimmune hepatitis and chronic hepatitis type C. These findings suggest less significance of anti-CA II antibody for the diagnosis of autoimmune pancreatitis and its hepatic involvements than as having been reported. However, the pathogenetic role of the antibody remains uncertain.