The cDNA of human interleukin-18 (hIL-18) was successfully inserted into the genome of tobacco plant, Nicotiana tabacum cv. NC-89, using Agrobacterium tumefaciens-mediated transformation. Insertion and translation of hIL-18 in transformants were confirmed by PCR, ELISA, and Western blot, respectively. The transformed extracts contained the recombinant hIL-18 protein up to 0.05% of total soluble protein. Activity of the recombinant hIL-18 in plant cells was confirmed by the induction of IFN-gamma on IL-18-responsive J6-1 cells by the extracts obtained from the transformants. The expression level of hIL-18 (351 ng g(-1) tobacco tissue) obtained in the present study may be sufficient to induce responses/effects in vivo.