In view of a recent spread of severe acute respiratory syndrome (SARS), there is a high demand for production of a vaccine to prevent this disease. Recent studies indicate that SARS-coronavirus (CoV) spike protein (S protein) and its truncated fragments are considered the best candidates for generation of the recombinant vaccine. Toward the development of a safe, effective, and inexpensive vaccine candidate, we have expressed the N-terminal fragment of SARS-CoV S protein (S1) in tomato and low-nicotine tobacco plants. Incorporation of the S1 fragment into plant genomes as well as its transcription was confirmed by PCR and RT-PCR analyses. High levels of expression of recombinant S1 protein were observed in several transgenic lines by Western blot analysis using specific antibodies. Plant-derived antigen was evaluated to induce the systemic and mucosal immune responses in mice. Mice showed significantly increased levels of SARS-CoV-specific IgA after oral ingestion of tomato fruits expressing S1 protein. Sera of mice parenterally primed with tobacco-derived S1 protein revealed the presence of SARS-CoV-specific IgG as detected by Western blot and ELISA analysis.