The use of prostaglandins in obstetrics has undergone a rapid evolution since their discovery in the early 1970s. It appears certain now that, at least in some cases, prostaglandins are important mediators of uterine activity. Indeed, a much stronger case can be made for the role of prostaglandins in labor than can be made for oxytocin. The pivotal role of prostaglandins in contraction of the smooth muscle of the uterus and the biophysical changes associated with cervical ripening, however, point to a major problem with their clinical use. Prostaglandins are produced by almost every tissue in the body and serve as important messengers or effectors in a wide variety of functions. Attempts to inhibit the production of prostaglandins to produce a reduction in myometrial contractility are limited by the important role of prostaglandins in maintenance of fetal ductal flow and renal blood flow. Similarly, administration of prostaglandins for the purpose of inducing labor or ripening an unfavorable cervix is tempered by the effects of these agents in other systems, including the gut and brain. Significant advances, however, have been made in the application of prostaglandins to common clinical problems in obstetrics. Of the multitude of products derived from the actions of cyclooxygenase on arachidonic acid, the most important for labor, delivery, and the postpartum period are the F and E series prostaglandins. Unlike oxytocin which requires an induction of receptors that does not usually occur until the later part of pregnancy, prostaglandins receptors always are present in myometrial tissue. This allows for the use of prostaglandins in usual doses throughout pregnancy. Although both F and E series prostaglandins result in uterine contractions, E series prostaglandins are relatively more uteroselective and are clearly superior to F series prostaglandins in producing cervical ripening. Modification of the naturally occurring prostaglandins by blocking the sites that are affected during their usual rapid metabolism, results in products with much longer durations of action, efficacy at much lower concentrations, and a potential for significant savings in cost. We are now able to manage efficiently problems such as intrauterine fetal death and intractable hemorrhage from postpartum uterine atony that often resulted in a surgical procedure prior to the availability of prostaglandin. We can continue to explore the potential of these agents in helping to solve the most difficult problems faced by the obstetrician.