The complete (encoding 55 amino acids, aa) or partial (encoding aa 1-26) preS2 region gene of hepatitis B virus (HBV) was fused to the 3＇-end of glutathion-S-transferase (GST) gene and expressed under the control of the inducible tac promoter in Escherichia coli at 37 degrees C. The fusion protein with the complete preS2 region was moderately expressed (8%) while the protein with the N-terminal 26 aa was expressed at a higher level, yielding about 20% of the total cellular proteins. The GST-preS2 (aa 1-26) protein, which contains the immunodominant epitope, was produced form the soluble protein fraction of the recombinant bacteria and purified by affinity chromatography using glutathione-agarose column. The purified preS2 fusion protein showed the antigenicity of preS2, as assessed by indirect and competitive ELISAs.