Hepatocyte stimulator peptide (HSP) is a new hepatic stimulator substance. Its monoclonal antibodies have been obtained in our laboratory. In this study, HSP was determined in the sera of 315 subjects including patients with various forms of hepatitis and healthy persons with enzyme-linked immunosorbent assay (sandwich method). It is shown that HSP level in the sera of patients with fulminant hepatitis was high and correlated with the level of tumour necrosis factor (TNF), serum bilirubin (SB) or prothrombin time (PT). It is suggested that level of HSP in the sera of the patients reflected the degree of hepatocyte injury. A formula was recommended to predict the outcome of the patients with fulminant hepatitis.