Objectives: To compare the effectiveness of 25 mug vs. 50 mug of intravaginal misoprostol for cervical ripening and labor induction beyond 41 weeks' gestation. Methods: The study population consisted of 120 women not in active labor with a gestational age > 41 weeks, singleton pregnancy with vertex presentation, reactive fetal heart rate tracing, amniotic fluid index greater than or equal to 5, and Bishop score < 5. Women were randomized to receive either 25 mug (n = 60) or 50 mug (n = 60) of intravaginal misoprostol. The dose was repeated every 4 h (maximum number of doses limited to six) until the patient exhibited three contractions in 10 min. The main outcome measure was the induction-vaginal delivery interval. Results: There was no significant difference between the two groups with regard to the induction-vaginal delivery interval (685 +/- 201 min in the 25 mug group vs. 627 +/- 177 min in the 50 mug group, P = 0.09). The proportion of women delivering vaginally with one dose of vaginal misoprostol was significantly greater in the 50 mug group (0/49 vs. 41/47, P <0.001). There were no differences in the rates of cesarean and operative vaginal delivery rates, or in the incidences of tachysystole and hyperstimulation syndrome in the two treatment groups. Neonatal outcomes were also similar. Conclusions: Intravaginal administration of 25 mug of misoprostol appears to be as effective as 50 mug for cervical ripening and labor induction beyond 41 weeks' gestation. (C) 2003 International Federation of Gynecology and Obstetrics. Published by Elsevier Science Ireland Ltd. All rights reserved.