LC1-Ab ELISA is a solid phase enzyme immunoassay employing human recombinant formiminotransferase- cyclodeaminase (cytosolic liver antigen) for the quantitative detection of anti-liver cytosol type 1 autoantibodies (anti-LC-1) in human serum. The assay is a tool for the diagnosis of autoimmune hepatitis (AIH). Autoimmune hepatitis (AIH) is a chronic progressive liver disease of unknown origin that responds well to immunosuppressive therapy, but has a poor prognosis if untreated. Early and accurate diagnosis is therefore of great importance. AIH is characterized by histological features of periportal hepatitis in the absense of viral markers, by hypergammaglobulinemia and, in the majority of patients, by the presence of autoantibodies in serum. Anti-nuclear antibodies (ANA), smooth muscle antibodies (SMA), anti-liver kidney microsomal antibodies (LKM) and antibodies against soluble liver antigen (SLA) are marker autoantibodies for AIH. 52% of AIH patients are positive for ANA and/or SMA, 20% for SLA and 3% for LKM-1. These antibodies are of diagnostic value for AIH but the only autoantibodies highly speci?c for AIH are SLA. ANA/SMA also occur in 10-15% of patients with viral hepatitis and other immunemediated diseases. LKM-1 are also associated with hepatitis C. Anti-LKM-1 associated AIH is less prevalent than ANA/SMA/SLA positive AIH and predominantly occurs in girls between 2 and 14 years of age. It has an acute onset with a rapid progression to cirrhosis and liver failure. Anti-liver cytosol type 1 autoantibodies have been reported in association with anti-LKM-1 autoantibodies in 30% of patients with LKM-1 positive AIH. In 10% of cases, anti-LC-1 antibodies are the only liver-related circulating autoantibodies. The antigen recognized by anti-LC1 has been identi?ed as a liver-specific 58 kDa metabolic enzyme named formiminotransferase cyclodeaminase (FTCD). FTCD is a bifunctional protein composed of distinct globular FT and CD domains connected by a short linker. The reactivity of anti-LC-1 autoantibodies is directed against multiple regions of the FTCD, mainly against conformation-sensitive epitopes in the FT region.