The aims of this study were to determine tumor necrosis factor-beta (TNF-beta) concentration profiles in peripheral venous plasma and amniotic fluid during pregnancy and at the time of labor and to characterise TNF-beta mRNA expression and TNF-beta release from human gestational tissues. In addition, we investigated the expression of TNF-beta binding protein, lymphotoxin-beta (LT-beta), in human gestational tissues. The mean (+/-S.E.M.) TNF-beta concentrations in maternal plasma (TIL, 78 +/- 12 pg/ml, n = 7 vs. TNIL, 304 +/- 88 pg/ml, n = 7) and amniotic fluid (TIL, 8 +/- 5 pg/ml, n = 6 vs. TNIL, 73 +/- 20 pg/ml, n = 20) were significantly (P < 0.05) decreased in association with term labor-onset (TIL) compared to term not-in-labor (TNIL). TNF-beta concentration in maternal plasma and amniotic fluid did not change significantly either with preterm labor (PIL), or during pregnancy. Group-matched comparison of maternal plasma and amniotic fluid TNF-beta concentrations demonstrated that amniotic fluid TNF-beta concentrations were 6-8 fold lower than maternal plasma TNF-beta concentrations. Furthermore, no detectable TNF-beta was secreted from cultured human amniotic, choriodecidual and placental explants. Although, TNF-beta mRNA was detected in amnion, choriodecidual and placenta, LT-beta was similarly expressed in these tissues, suggesting that TNF-beta may be cell membrane bound. These data demonstrate that TNF-beta is present at low levels within the intrauterine environment and may suggest that TNF-beta is specifically inhibited at the maternal-fetal interface.