OBJECTIVES: The purpose of this study was to determine whether a concentrated oxytocin infusion can reliably effect uterine evacuation in the midtrimester and whether such an infusion is associated with fewer side effects than prostaglandin E2 vaginal suppositories. TUDY DESIGN: Patients received either prostaglandin E2 (n = 42) or oxytocin (n = 45) for indicated midtrimester abortions in a prospective, randomized trial. Treatment consisted of either prostaglandin E2 vaginal suppositories (one every 4 hours) or infusions of an escalating concentration of oxytocin (one every 4 hours). Unless delivery had occurred or was imminent after 24 hours, the agent was considered to have failed, and patients were crossed to the alternative method. RESULTS: Delivery indications were similar between the two groups. There were 6 (14%) first-agent failures with prostaglandin E2 and 9 (20%) with oxytocin (p = 0.48). Considering the failures and subsequent crossovers, 103 patient trial regimens were completed. Fever, nausea, vomiting, and diarrhea were more frequent with prostaglandin E2 (p < 0.005). CONCLUSIONS: Concentrated oxytocin is a satisfactory alternative to prostaglandin E2 for midtrimester abortion. (Am J Obstet Gynecol 1992;167:1112–6.) © 1992, Mosby. All rights reserved.