LKM-1-Ab ELISA is a solid phase enzyme immunoassay employing human recombinant cytochrome p450 IID6 for the quantitative detection of antibodies against liver-kidney microsomes (LKM) 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 specific 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. Three types of LKM antibodies can be distinguished according to the target antigens. LKM-1 antibodies are directed against cytochrome p450 IID6, a 50 kDa cytoplasmic protein found in hepatocytes and renal proximal tubular cells. LKM-2 antibodies are associated with ticrynafen (tienilic acid) –induced hepatitis. The target antigen is cytochrome p450 IIC9, a cytochrome p450 isoenzyme that catalyzes the metabolic oxidation of the drug. LKM-3 antibodies are associated with chronic hepatitis D. The target antigen is UDP-1 glucoronosyl transferase. LKM-1 associated AIH predominantly occurs in girls between 2 and 14 years of age, thus determination of LKM-1 is very important in pediatrics.