The expression of infectious bronchitis virus (IBV) S1 glycoprotein in potatoes and its immunogenicity in mice and chickens were investigated. Potato plants were genetically transformed with a cDNA construct encoding the IBV S1 glycoprotein with the Agrobacterium system. Genomic DNA and mRNA analyses of the transformed plantlets confirmed the integration of the foreign cDNA into the potato genome, as well as its transcription. Mice and chickens vaccinated with the expressed IBV S1 glycoprotein produced antibodies that neutralized IBV infectivity. After three immunizations, vaccinated chickens were completely protected from virulent IBV infection. These results demonstrate that transgenic potatoes expressing IBV S1 glycoprotein can be used as a source of recombinant antigen for vaccine production.