Porcine tumor necrosis factor alpha (TNF-alpha) was produced using a baculovirus system in Spodoptera frugiperda (SF21AE) cells. Cytotoxic activity was detected in supernatant of sonicated SF21AE cells infected with recombinant viruses. The recombinant protein was also demonstrated to be functionally active by its ability to cause apoptosis in Wehi 164 cells. Three distinct bands of 26, 17 and 14 kDa were revealed by Western blot analysis using anti-human TNF-alpha antibody. Moreover, the anti-human TNF-alpha antiserum significantly neutralized the cytotoxic activity of the supernatant of sonicated SF21AE cells infected with recombinant viruses.