We investigated the existence and possible role of cytosolic phospholipase A2 (cPLA2) in rat decidualized uteri. PLA2 activity in the cytosol of a decidualized uterine horn, induced by intraluminal oil infusion, was significantly higher than that in contralateral intact horn. The activity was almost completely depressed by cPLA2 inhibitors including arachidonyl trifluoromethyl ketone (ATK). The immunoreactive signals for cPLA2 were intense in decidua and glandular epithelial cells. In vivo administration of ATK (0.1-100 microg) caused a dose-dependent inhibition of decidualization. These results show the presence of cPLA2 and its probable implication in decidualization in rat uterus.