Phylogenetic tree of HBV isolates constructed with the neighbor-joining method, and based on the nucleotide sequences of the entire pre-S/S region (nt positions 2854 to 833). Isolates whose names begin by 1,2,3 were molecular clones from this study derived from samples collected in 1999, 2001, and 2002, respectively. The other isolates are designated by their GenBank accession numbers. Genotype A isolates clustered in two subgroups, designated A-A' (genotype A excluding A') and A' . The sequence AY090458 belongs to genotype F and was used as an outgroup. Numbers at internal nodes indicate percentage of 100 bootstrap replicates that support the branch. Only values > 85% are indicated. The horizontal bar provides a genetic distance.