The role of cellular immune responses in mediating hepatocyte injury of virus-infected cells is under active investigation. Induction of humor immunity to viral protein antigens may be important in hepatitis viral clearance from the host. Studies defining the critical epitopes on hepatitis B viral proteins that stimulate both B-and T-cell response are emerging. Interferon therapy is being used to treat individuals with chronic hepatitis B and C infection and may have effects on inhibiting viral replication and enhance HLA class I expression on hepatocytes as well as modulate B-and T-lymphocyte function. Detection of antibodies produced against hepatitis viral proteins and hepatocyte cellular antigens have become important in the diagnosis of acute and chronic active hepatitis.