The nucleocapsid of the hepatitis B virus is covered by an envelope of HBV surface antigen (HBsAg), which has the common, group-specific determinant a. The four major subtypes of HBsAg, adw, adr, ayw and ayr, are generated, and they have been proposed to represent the phenotypic expression of the four major genotypes of HBV1. HBsAg subtypes show distinct geographical distributions2 and may provide historical information on the migration of ancestors carrying HBV of a particular subtype3.