Antibody binding to living Chang liver cell was measured in sera from 71 patients with various chronic liver diseases using 125I-labelled protein A binding assay. The level of antibody binding to Chang liver cell was significantly elevated in sera from patients with chronic active hepatitis (CAH), chronic persistent hepatitis (CPH) and liver cirrhosis as compared to those from healthy donors, but not in sera from patients with fatty liver. There was no detectable antibody binding to HeLa cells in those sera. The antibody binding to Chang liver cell was blocked by a human liver specific protein (LSP) preparation. The levels of antibody binding to Chang liver cell were significantly higher in patients with CAH than patients with CPH. On the other hand, the level of antibody binding to Chang liver cell was significantly decreased in sera from patients with CAH after a treatment with prednisolone (PSL) for 2 months and a subsequent combined administration of 6MP and a maintenance dose of PSL for 1 month. These results suggest that antibodies to Chang liver cell are closely correlated with the activity of chronic liver disease and that PSL and 6MP treatment can reduce the level of the antibodies.