Intrauterine infection is an important cause of preterm labor and delivery and is characterized by increased production of inflammatory cytokines by gestational tissues. We have evaluated the biosynthesis of the inflammatory cytokine, interleukin-6 (IL-6), by human decidua and its regulation by other cytokines essential to the inflammatory process. We found that decidual cells secrete small amounts of IL-6 in the presence of growth medium supplemented only with 10% fetal calf serum. Interleukin 1 (alpha and beta) and tumor necrosis factor (TNF) all induced a significant concentration-dependent stimulation of IL-6 production by decidual cells. Treatment of decidual cells with actinomycin D or cycloheximide abrogated the increase in IL-6 production induced by IL-1 beta. Northern blot analysis of cultured decidual cells revealed an increase in IL-6 messenger RNA (mRNA) over time in response to IL-1 beta. These data indicate that IL-1 beta stimulates an increase in IL-6 mRNA and protein production, reflecting either direct gene activation or stabilization of IL-6 mRNA. The concentration range tested (0.1 to 10 ng/mL) of each cytokine is within the range of values found in the amniotic fluid of women destined to deliver preterm due to infection of gestational tissues. Our data suggest that IL-6 is produced by human decidua in response to inflammation and, in conjunction with other inflammatory mediators, may play a role in the pathophysiology of preterm labor due to infection.