The antibody, and its immunoglobulin class, against endotoxin (LPS ; E. coli 026 : B6) in sera from patients with various liver diseases was examined by the use of an enzyme-linked immunosorbent assay (ELISA). The IgG-antibody titer to endotoxin was high in sera from patients with liver cirrhosis (LC), fulminant hepatitis (FH), severe chronic active hepatitis (CAH2B), alcoholic hepatitis and acute hepatitis (AH), and its titer was associated with the severity of liver injury. The IgA-antibody titer was high in sera of patients with alcoholic hepatitis, FH, LC, CAH2B and AH. The patient with the highest titer had alcoholic hepatitis. The IgM-antibody titer was not associated with the severity of liver injury, but it was associated with the acute stage of acute hepatitis and acute exacerbation of chronic hepatitis. The antibody titer was higher in sera of LC patients with ascites and/or esophageal varices than in LC patients without them (especially IgA-antibody : p>0.01). The ELISA for detection of antibody to endotoxin was useful for clinical observation of patients with liver diseases.