The work was carried out to analyze variability in §the immunogenic regions of surface envelope genes of §Pakistanian Hepatitis B virus isolates. The PreS §region, the hypervariable and highly immunogenic §region, containing at least five epitopes, was PCR §amplified, cloned and sequenced. Sequence §alighnments and comparisons with other known HBV §sequences from different parts of the world were §performed in order to build a phylogenetic tree and §to check if certain amino acids mutations tend to §recur in certain places within the hypervariable §region. On the basis of...