The present study was performed to determine whether estradiol, via cAMP mediation, induces prostaglandin synthesis by modulating phospholipase A₂ activity which hydrolyzes phospholipids into arachidonic acids, a precursor for prostaglandin synthesis, during the implantation process in rats. Uterine phospholipase A₂ activity was elevated on day 5 of pregnancy when implantation normally occurs in rats. Moreover, phospholipase A₂ activity was higher in the implant sites than in the non-implant sites of uterus on day 6. In delayed implantation model, phospholipase A₂ activity was increased at 12 hrs after estradiol administration and at 8 hrs after dbcAMP administration. In addition, higher activity of phospholipase A₂ was induced by the treatment of estradiol plus theophylline, compared with estradiol-only treated group. The simultaneous treatment of indomethacin with estradiol or dbcAMP did not alter phospholipase A₂ activity compared with estradiol or dbcAMP-only treated group although significant suppression was observed in uterine PGE and PGE_2α concentrations. These results suggest that estradiol or cAMP stimulates uterine phospholipase A₂ activity, thereby increasing prostaglandin synthesis during the implantation process in rats.