OBJECTIVE: To compare the efficacy and safety of two prostaglandin derivatives, misoprostol and dinoprostone, for ripening the cervix and inducing labor in women with an unfavorable cervix. METHODS: One hundred fifty-five women admitted for induction of labor to St. John's Mercy Medical Center, a teaching community hospital, were randomized to one of two methods: intravaginal misoprostol, 50 microg every 4 hours up to three doses (n = 76); and intracervical dinoprostone gel, 0.5 mg every 6 hours up to three doses (n = 79). RESULTS: Misoprostol was more effective than dinoprostone in causing cervical ripening (P = .01), inducing labor (P < .001), shortening the duration of labor (P < .001), and decreasing the need for oxytocin augmentation (P < .001). Nonreassuring fetal heart monitoring patterns associated with hyperstimulation were significantly more frequent (P < .001), and the incidence of cesarean deliveries because of this indication was significantly higher (P = .002) in patients receiving misoprostol. CONCLUSIONS: Misoprostol is an effective agent for cervical ripening and labor induction, but it causes an increase in cesarean deliveries associated with uterine hyperstimulation.