We describe the secretory expression and immunogenicity of the recombinant HAV (hepatitis A virus) structural polypeptide VP1 from stably transformed Drosophila melanogaster S2 (Schneider 2) cells. Southern-blot analysis indicated that transformed S2 cells contained multiple copies of the HAV VP1 gene in the genome. Recombinant VP1 was secreted into a culture medium with a molecular mass of 42-49 kDa. A maximum production level of 6.24 mg of recombinant VP1/litre was obtained in a T-flask culture of Drosophila S2 cells 5 days after induction with 0.5 mM CuSO4. The recombinant HAV VP1 protein elicited the production of specific IgA in the small intestine by oral immunization and production of specific IgG in the serum by intraperitoneal immunization. Our findings show that secretory recombinant VP1 from transformed Drosophila S2 cells can be used as an effective experimental immunogen for research in vaccine development.