Viral hepatitis is a major public health problem occurring endemically in all parts of the world. The general term viral hepatitis refers to infections caused by hepatitis virus type A, type B and a more recently identified infection referred to as "non-A: non-B" hepatitis. These clinically and pathologically similar forms of hepatitis have been studied intensively following the discovery of a specific antigen, Australia antigen, one of the markers of infection with hepatitis B virus.