Recently, it has been demonstrated that plants offer the possibility of producing low cost subunit vaccines that can be either parenterally or orally administered. Here we review data we obtained on the immunological response elicited by two recombinant versions of the glycoprotein S from the swine transmissible gastroenteritis coronavirus (TGEV) expressed in transgenic plants. Arabidopsis or potato plants were genetically transformed with cDNAs constructs encoding the N-terminal domain (aa residues 1–750) or the full-length glycoprotein S of TGEV, responsible for the neutralizing antibody induction against the virus, under the control of the cauliflower mosaic virus 35S (CaMV 35S) promoter. Genomic DNA and mRNA analysis of leave extracts from transformed plants demonstrated the incorporation of the foreign cDNA into the plant genomes as well as their transcription. Expression of recombinant polypeptides was observed in most transgenic plants by ELISA using specific antibodies. Mice immunized either parenterally with leave extracts from transgenic arabidopsis plants or, more interestingly, fed with potato tubers, developed antibodies that specifically reacted with TGEV in ELISA, immunoprecipitated the glycoprotein S and in some cases neutralized the virus infectivity. From the above results, we conclude that transgenic plants expressing glycoprotein S polypeptides may be potentially used as a source of recombinant antigen for vaccine production.