We investigated the existence and possible role of cytosolic phospholipase A 2 (cPLA 2 ) in rat decidualized uteri. PLA 2 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 cPLA 2 inhibitors including arachidonyl trifluoromethyl ketone (ATK). The immunoreactive signals for cPLA 2 were intense in decidua and glandular epithelial cells. In vivo administration of ATK (0.1-100 μg) caused a dose-dependent inhibition of decidualization. These results show the presence of cPLA 2 and its probable implication in decidualization in rat uterus.