The effect of recombinant porcine interferon-gamma (rPoIFNγ) on in vitro production of interleukin 1 (IL-1) by porcine blood monocytes was studied. Three-day-old cultures of porcine adherent blood mononuclear cells were treated by doses of rPoIFNγ for 3 or 6 days before lipopolysaccharide (LPS)-induction. While rPoIFNγ alone had no effect, a combined treatment by rPoIFNγ and LPS enhanced the IL-1 secretory potential of adherent mononuclear cells and, to a lesser extent, the level of cell-associated IL-1. The IL-1 activity was neutralized by anti porcine IL-1 α and β antisera. These results demonstrate that rPoIFNγ has immunomodulatory effects in vitro on porcine monokine production.