Arachidonic acid mobilization by phospholipase A2 (PLA2) and subsequent prostaglandin synthesis is thought to be a pivotal event in the onset and/or maintenance of human labour. The purpose of this study was to quantify secretory PLA2 (sPLA2) and non-secretory PLA2 enzymatic activity and type II sPLA2 immunoreactivity in human gestational tissues before, during and after labour of spontaneous onset. Placental tissue and fetal membranes were collected from women before, during and after spontaneous-onset labour at term and stored at - 80 degrees C. PLA2 activity in supernatants was quantified by radiolabelled substrate assay (14C-phosphatidylethanolamine) with and without 12.5 mm dithiothreitol (DTT) to separate enzymatic activity contributed by secretory and non-secretory PLA2 components. Immunoreactive type II PLA2 in supernatants was determined by a monoclonal, non-competitive sandwich ELISA. Total PLA2 enzymatic activity in amnion, choriodecidua and placenta was not significantly different before, during and after labour (n=18-20). Likewise, non-secretory enzymatic activity was not significantly different before (n=9), during (n=10) and after labour (n=9) in any of the three types of gestational tissue examined. Although immunoreactive type II PLA2 was significantly higher in the placenta (P<0.01) compared to amnion and choriodecidua, there was no significant difference in immunoreactive type II PLA2 within each tissue group according to labour status (n=18-20). Overall, no change in PLA2 secretory or non-secretory enzymatic activity or immunoreactive type II PLA2 could be detected throughout the peripartum period.