Since the discovery of Australia antigen and its association with type B
hepatitis, molecular characterization of the components making up
hepatitis B virus (RBV) have been pursued with worldwide interest. Over
the past two decades, such characterization has led to the development
of sensitive assays to screen and exclude contaminated units from blood
banks and has recently resulted in the licensing of several RBV
vaccines. That more than 200 million people worldwide are chronically
infected with RBV, and that they are at a high risk for the development
of chronic hepatitis and hepatocellular carcinoma, still represent
formidable problems in our understanding of host-virus relationships on
the molecular level. In the absence of a suitable tissue culture system,
and with a very limited host range of infection, characterization of RBV
on the molecular level has made remarkable progress recently with the
advent of genome cloning, sequencing and expression of individual virus
genes by recombinant DNA technology. The presence of hepatitis B-like
viruses in an expanding number of animal hosts, and the possibility of
virus replication in cells other than hepatocytes, provide great promise
that future work will elucidate the molecular mechanisms operative in
the various outcomes of RBV infection.