OBJECTIVE Our purpose was to compare the safety and efficacy of intravaginal misoprostol versus intracervical prostaglandin E2 (dinoprostone) gel for preinduction cervical ripening and induction of labor. METHODS One hundred thirty-five patients with indications for induction of labor and unfavorable cervices were randomly assigned to receive either intravaginal misoprostol or intracervical dinoprostone. Fifty microgram tablets of misoprostol were placed in the posterior vaginal fornix every 3 hours for a maximum of six doses. Prostaglandin E2 in gel form, 0.5 mg, was placed into the endocervix every 6 hours for a maximum of three doses. Medication was not given after either spontaneous rupture of membranes or beginning of active labor. RESULTS Among 135 patients enrolled, 68 received misoprostol and 67 received dinoprostone. The average interval from start of induction to vaginal delivery was shorter in the misoprostol group (903.3 +/- 482.1 minutes) than in the dinoprostone group (1410.9 +/- 869.1 minutes) (p < 0.001). Oxytocin augmentation of labor occurred more often in the dinoprostone group (65.7%) than in the misoprostol group (33.8%) (p < 0.001). There were no significant differences between routes of delivery. Ten of the misoprostol-treated patients (14.7%) and 13 of the dinoprostone-treated patients (19.4%) had cesarean deliveries. There was a higher prevalence of tachysystole (six or more uterine contractions in a 10-minute window for two consecutive 10-minute periods) in the misoprostol group (36.7%) than in the dinoprostone group (11.9%) (p < 0.001). However, there were no significant differences in frequency of uterine hyperstimulation or hypertonus. There was a higher prevalence of meconium passage in the misoprostol group (27.9%) than in the dinoprostone group (10.5%) (p < 0.05). There was no significant difference in frequency of abnormal fetal heart rate tracings, 1- or 5-minute Apgar scores < 7, neonatal resuscitations, or admissions to the neonatal intensive care unit between the two groups. CONCLUSIONS Vaginally administered misoprostol is an effective agent for cervical ripening and induction of labor; however when given at this dosage, it is associated with a higher prevalence of tachysystole and meconium passage than is dinoprostone. Further studies to compare the safety of misoprostol to that of dinoprostone and to delineate an optimal dosing regimen for misoprostol are needed.