We investigated the effects of transforming growth factor beta (TGF beta) on the induction by interleukin-1 beta (IL-1 beta) of IL-6 in human monocytes. We found that IL-1 beta induced IL-6 messenger RNA expression in elutriated monocytes and IL-6 secretion in the supernatant. TGF beta did not induce IL-6. In contrast, TGF beta added to the culture inhibited, in a dose-dependent manner, the induction of IL-6 by IL-1 at the level of messenger RNA and bioactivity. These results show that IL-1 beta is able to stimulate IL-6 production by monocytes, TGF beta, by inhibiting this effect, may play an important role in regulating the IL-1-mediated components of the inflammatory response.