Autoimmune hepatitis is associated with genes located in the major histocompatibility complex. The search for genes at other loci that may play a role in disease susceptibility and/or severity is an area of active investigation in autoimmune liver diseases. Genes for glutathione-S-transferases, enzymes that are widely distributed and collectively metabolize carcinogens, pollutants, drugs, and a broad spectrum of harmful, foreign compounds have been associated with liver disease. The objective of this study was to search for a relationship between the glutathione-S-transferase Ml null genotype and autoimmune hepatitis using polymerase chain reaction analysis. The findings indicate that the frequency of the null genotype is not increased in patients with autoimmune hepatitis when compared to control subjects. These results coupled with similar ones in primary biliary cirrhosis do not support a role for this mutation in autoimmune liver disease.