Humoral and/or cell-mediated (CMI) immune responses to HBAg components, human and rabbit liver specific proteins (HLP and RLP) and tuberculin were tested in patients with acute virus B and non-B-hepatitis, asymptomatic HBsAg carriers and HBsAg positive chronic active hepatitis (CAH). Furthermore, the presence of HBsAg, HBcAg and/or "e"-antigen has been studied in patients with sera and/or liver tissue. Asymptomatic HBsAg carriers are characterized by a status of immunological tolerance against HBsAg. HBcAg in liver nuclei could not be detected. All sera were positive for anti-HBc, some had anti "e". - Patients with uneventful acute virus-B-hepatitis developed CMI against HBsAg 4-6 weeks and anti-HBs 4-6 months after onset of the disease. Acute virus hepatitis without detectable HBsAg are defined as non-B-hepatitis by negative humoral and cell-mediated immune reaction against HBsAg 1-12 months after onset of the disease. - Patients with type B chronic active hepatitis are characterized by inadequate CMI against HBsAg without immune elimination of virus and virusantigens. Acute and chronic type-B-hepatitis showed temporary or constant CMI against HLP. These findings suggest an alteration or a carrier function of membrane antigens of virus infected hepatocytes or an induction of new membrane antigens by a virus. The results indicate that recovery from type B-hepatitis is associated with the ability to elicit a specific immune response to HBsAg. Furthermore immune responses to virus, virus antigens and virusinfected hepatocytes seemed to be the pathogenic principle of virus induced acute and chronic liver diseases.