The abnormal degradation of the extracellular matrix by matrix metalloproteinases (MMPs) in the fetal membranes has been proposed as a central event in preterm premature rupture of the membranes (pPROM). Prostaglandins (PGs) are thought to increase the risk of preterm premature rupture of the fetal membranes by causing matrix degradation. The aim of this study was to assess the mediating role of PGs on lipopolysaccharide (LPS)-induced MMP9 secretion in vitro. ELISA, zymography, and Western blotting were performed on cells and medium from cultures of purified chorion trophoblasts (CTs) and syncytiotrophoblasts (STs) from the human placenta and fetal membranes treated with LPS, meloxicam, (a selective prostaglandin-endoperoxide synthase 2 [PTGS2, previously known as cyclooxygenase 2] inhibitor), or replacement PGE₂ or PGF_2alpha. LPS significantly (P < 0.01) increased proMMP9 secretion and prostaglandin E₂ (PGE₂) output by cultured CTs and STs, but there was no effect on tissue inhibitor of matrix metalloproteinase 1 (TIMP1) secretion. In these cells, meloxicam significantly blocked LPS-induced proMMP9 secretion and PGE₂ output (P < 0.01). Exogenous PGE₂ and PGF_2alpha significantly reversed the reduction in proMMP9 secretion caused by meloxicam in a dose-dependent manner (P < 0.01). The expression of PTGS2 protein in CTs and STs was increased dramatically after LPS treatment, but there was no significant effect on the expression of PTGS1 (previously known as cyclooxygenase 1), membrane-associated prostaglandin E synthases (membrane-associated PTGES, previously known as mPGES) 1 and 2, or cytosolic prostaglandin E synthase (cytosolic PTGES, previously knows as cPGES) proteins. Our results suggest that PGs may mediate the selective increase in MMP9 after exposure of trophoblast cells to LPS. There was no effect of LPS on TIMP1. Understanding this relationship may help in developing strategies for the prevention and management of pPROM and preterm labor.