PreS2/S vaccination of chronic hepatitis B virus (HBV) carriers led to a reduction in HBV replication or clearance of virus in 30% of treated patients. This study assessed whether vaccinotherapy of chronic HBV carriers induced the selection of escape mutants in the envelope 'a' determinant and whether envelope genetic variability might affect the response to vaccination. No amino acid differences were observed in the 'a' determinant between sequences obtained before and after treatment (five responders and seven non-responders). However, alignment with HBV prototype sequences revealed seven amino acid changes. Two mutations (T140S and P127L) diverged from subtype variations. In the complete envelope sequence (five non-responders and five responders), ten amino acid modifications were detected between sequences obtained before and after treatment. The absence of any common mutations did not enable the definition of a hot spot of mutations implicated in the response to vaccination. Moreover, vaccinotherapy does not induce the selection of escape mutants in the 'a' determinant.