Objective: To determine whether leaving the membranes intact in active-phase arrest would affect the cesarean delivery rate or the incidence of maternal morbidity secondary to infection. Methods: We conducted a randomized trial of healthy, spontaneously laboring women at term with an intact chorioamnion and active-phase arrest (defined as 1 cm or less of cervical change over 2 hours in the active phase of labor). Patients were assigned to either oxytocin augmentation with intact chorioamnion or oxytocin augmentation with amniotomy and internal monitoring of the fetal heart rate and uterine contractions. Results: The intact group (n = 58) and the amniotomy group (n = 60) were similar with respect to maternal age, race, parity, labor epidural usage, gestational age, cervical dilatation at randomization, number of vaginal examinations, and infant birth weight. Four patients in the intact group and five in the amniotomy group underwent cesarean delivery (P = 1.0). No patients in the intact group and three in the amniotomy group were diagnosed with chorioamnionitis (P = .24). Endometritis did not occur in the intact group, whereas four cases occurred in the amniotomy group (P = .12). There were no cases of maternal infection in the intact group, versus seven in the amniotomy group (P = .01). The interval between randomization and vaginal delivery was 44 minutes longer in the intact group than in the amniotomy group (P = .11). Conclusion: In women with active-phase arrest of labor and intact membranes, oxytocin augmentation with elective amniotomy and internal monitoring increases maternal infectious morbidity. © 1995 The American College of Obstetricians and Gynecologists.