The objective of this study was to examine the expression and activity of cytosolic phospholipase A 2 (cPLA 2) in relation to prostaglandin E 2 (PGE 2) synthesis in human amnion-derived WISH cells in response to stimulation by interleukin-1β (IL-1β). cPLA 2 activity was characterized by sensitivity to heat and acid treatment, stability to dithiothreitol, and inhibition by the specific inhibitor, arachidonyl trifluoromethyl ketone (AACOCF 3). Treatment of WISH cells with IL-1β (0.01–1 ng/mL) for up to 24 h resulted in a significant increase in PGE 2 release in a concentration- and time-dependent manner accompanied by increases both in total cellular cPLA 2 activity and in cPLA 2 protein levels detected by Western blot analysis. The parallel increase in total cellular cPLA 2 activity and cPLA 2 protein level indicates that IL-1β may induce the synthesis of CPLA 2. Incubation of the cells with 10 μM AACOCF 3 for 24 h significantly inhibited IL-1β-induced PGE 2 production strongly suggesting that cPLA 2 mediates IL-1β-induced PGE 2 formation. In unstimulated cells, there is appreciable total cellular cPLA 2 activity and protein, but these cells produce low amounts of PGE 2 until stimulated by IL-1β, suggesting that cPLA 2 translocation from cytosol to the membrane is necessary for its bioactivity. In contrast to IL-1β, treatment with phorbol ester (12-O-tetradecanoyl phorbol-13-acetate, TPA, 10 −10−10 −6 M) for 24 h significantly inhibited total cellular cPLA 2 activity in a concentration-dependent manner. The amount of total cellular cPLA 2 protein seen on Western blot remained unchanged following TPA treatment. These data suggest that in WISH cells, IL-1β induces both translocation to the membrane and de novo synthesis of cPLA 2 protein to sustain prostaglandin (PG) synthesis. In contrast, TPA may only cause cPLA 2 translocation but no increase in cPLA 2 protein synthesis, resulting in limited PFG synthesis. Our results provide a mechanism for the effect of IL-1β on prostaglandin synthesis in human amnion cells and provide support for a role of cPLA 2 in the mechanism initiating human parturition.