Objective: To compare the effectiveness of 400 mug rectal misoprostol in 5 cm(3) of saline with oxytocin 10 IU, i.m., in reducing bleeding during the third stage of labor. Design: A double blind, randomized, clinical trial including 663 women with uncomplicated vaginal delivery who received misoprostol (n = 324) or oxytocin (n = 339). Main outcome measures: Changes in hemoglobin and hematocrit from before to 72 h postpartum; blood loss during the third stage; duration of the third stage of labor; need for additional oxytocic drug; frequency of requisition and of administration of blood; changes in blood pressure; and occurrence of side effects. Results: No significant differences were observed between groups, before and 72 h postpartum, in mean hemoglobin and hematocrit, on volume of blood loss and duration of third stage of labor. The incidence of shivering and mean temperature (P < 0.01) was significantly greater among women receiving misoprostol than oxytocin. Conclusions. Misoprostol administered as a micro-enema, 400 mug in 5 mi of saline during the third stage of labor, appears to be as effective as oxytocin 10 IU, i.m., but misoprostol produced more side effects than oxytocin. (C) 2001 International Federation of Gynecology and Obstetrics. All rights reserved.73116