OBJECTIVE The purpose of this study was to determine if prostaglandin E2 in a controlled-release vaginal pessary can produce cervical ripening at term. METHODS This was a double-blind, randomized, placebo-controlled study conducted at a university center and involving 81 patients with 42 receiving active agent. Categoric data were analyzed by Pearson's chi 2 or logistic regression. Continuous variables were analyzed by analysis of variance and the F test. RESULTS Prostaglandin E2 was significantly better than placebo at cervical ripening and at decreasing the time to rupture of membranes, the time to onset of labor, the need to give oxytocin, and the time to vaginal delivery. Multiparous women benefitted more than primiparous ones. The cesarean section rate decreased only for multiparous women. Uterine hyperstimulation occurred only with prostaglandin E2 and after the onset of labor. CONCLUSIONS Prostaglandin E2, when administered in a controlled-release vaginal pessary, is affective in producing cervical ripening at term. This agent should be used on inpatients who are under continuous monitoring and it should be removed at the onset of labor.