Antibodies that react against specific structures in cells can be demonstrated by immunofluorescent technique. Antimitochondrial antibodies are found in 80%-100% of biliary cirrhosis patients and may aid in the diagnosis of this uncommon disease. False positive results have been reported in some patients with drug-induced cholestasis and chronic active hepatitis, as well as in a relatively small number of patients with extrahepatic obstruction, acute infectious hepatitis, rheumatoid arthritis, and other conditions. There are subgroups of antimitochondrial antibodies; the M-2 subgroup is claimed to be specific for primary biliary cirrhosis. However, it is very difficult to obtain testing for M-2 alone. Anti-smooth muscle antibodies were reported in 45%-70% of patients with chronic active (“lupoid”) hepatitis but have also been found in biliary cirrhosis and, less frequently, in other liver diseases (except alcoholic cirrhosis). An immunofluorescence expert is needed to set up and interpret these procedures. Liver biopsy is still needed.