Three plasmid expression vectors containing modified hepatitis B surface antigen (HBsAg) carrying pres epitopes were constructed. Transient expression after in vitro transfection in COS-M6 cells showed that under the transcriptional control of the human cytomegalovirus (CMV) immediate early promoter, fusion genes expressed the modified HBV envelope proteins which were efficiently secreted into culture medium and presented HBsAg, preS1 and preS2 antigenicity. DNA-based immunization with these plasmids carrying pres sequences induced anti-HBs antibody in BALB/c mice. The titers of anti-HBs antibody were higher than those appeared in mice immunized with plasmid carrying S gene only. DNA injection with plasmids containing preS1 sequences elicited also high titers of anti-preS1 antibody. Moreover, the antipreS1 antibodies were found to appear earlier than anti-HBs antibodies. Three plasmid expression vectors containing modified hepatitis B surface antigen (HBsAg) carrying pres epitopes were constructed. Transient expression after in vitro transfection in COS-M6 cells showed that under the transcriptional control of the human cytomegalovirus (CMV) immediate early promoter, fusion genes expressed the modified HBV envelope proteins which were effectively secreted into culture medium and presented HBsAg, preS1 and preS2 antigenicity. DNA-based immunization with these plasmids carrying pres sequences induced anti-HBs antibody in BALB / c mice. The titers of anti-HBs antibody were higher than those had in mice immunized with plasmid carrying S gene only. The antipreS1 antibodies were found to be earlier than anti-HBs antibodies.