Hepatitis B-virus (HBV) infection is a world-wide health problem especially in the Far-East and Africa. A person with chronic HBV infection has a 200- fold higher risk of developing hepatocellular carcinoma and cirrhosis as compared to a non-carrier individual. Vaccines for HBV are widely available, however, for the HBV-infected individual there is no means of arresting the progress of the disease due in part to our lack of knowledge of how HBV enters the host cells. DNA sequence coding for the preS1 peptide of the surface antigen was inserted in an expression plasmid and large quantities of preS1 peptide as purified from E. coli. The isolated preS peptide was able to bind specifically but weakly to the isolated plasma membranes from human liver (Lin et al., 1991). Recent reports indicated that other parts of the surface antigen might also be important for the receptor binding. Experiments are in progress to express the entire surface antigen in a baculoviral expression system. The large surface antigen will be used for receptor binding studies.