Abstract: It has been postulated that hormonal signal acts upon decidua and ammion totrigger labor via production of PGs.In our experiment the decidua cells of pregnant rats(day 19)were digested and dispersed to test the effect of oxytocin on intracellular calcium ion concentrationCa²⁺i which was measured with the fluorecent dye fura-2. Addition of oxytocin 0.001～1μmol·L^-1 to the test system resulted in a dose-dependent transient increase in Ca²⁺i which peakedwithin l5s and returned to base line in i2min.Repeated addition of oxytocin 1 μmol·L^-1failed toelicit a repeated response.In the decidua cells of dihydroepiandroterone sulfate-treated pregnant rats,theCa²⁺i peak provoked by oxytocin was significantly higher than in the controls.These resultssuggest that oxytocin may activate the incositol-phospholipid-protein kinase C effector system in deciduacells of prgenant rats.Dihydroepiandrosterone sulfate may influence the action.