OBJECTIVE: This study was undertaken to determine whether subchorionic endotoxin infusion causes chorioamnionitis and preterm lung maturation, as occurs after intra-amniotic endotoxin.STUDY DESIGN: From day 118 of pregnancy, sheep received infusions of endotoxin (subchorionic 7.5 mg/d, n = 11; intra-amniotic 2.5 mg/d, n = 9) until delivery of lambs at 120 or 124 days. Other sheep received a single intra-amniotic injection of endotoxin (10 mg, n = 7) at 118 days before delivery at 124 days. Controls (n = 9) received equivalent saline solution treatments.RESULTS: Chorioamnionitis accompanied all endotoxin treatments. Lung inflammation occurred after intra amniotic endotoxin infusion or injection but not after subchorionic endotoxin. Umbilical arterial pH was lower and Pco(2) was higher than control after subchorionic endotoxin. Lung compliance and surfactant were increased after intra-amniotic endotoxin infusion or injection but not after subchorionic endotoxin.CONCLUSION: Chorioamnionitis may result from inflammatory stimuli at various intrauterine sites, with different sites causing different fetal effects and not all cases of chorioamnionitis being accompanied by enhanced lung maturation.