Halogenated anesthetic agents have been used to supplement nitrous oxide during balanced general anesthesia for cesarean delivery to decrease maternal awareness. However, these agents can interfere with uterine contractility and hence have the potential to increase blood loss at the time of cesarean section. To ascertain the effect of the addition of halogenated anesthetic agents for cesarean section anesthesia versus conduction or a simple balanced general anesthetic, we retrospectively assessed three aspects that may reflect operative blood loss at the time of cesarean section. Significantly more women whose balanced general anesthesia for cesarean section was supplemented with a halogenated agent (usually 0.5% halothane) versus those with a conduction or balanced general anesthetic required transfusion therapy, had a postpartum hematocrit less than 30 vol % and had a decrease in the pre- to postdelivery hematocrit of at least 8 vol %. The addition of halogenated anesthetic agents to a balanced nitrous oxide anesthesia for the purpose of decreased maternal awareness must be weighed against the risk incurred from the increased requirement for blood replacement and/or from postpartum anemia. © 1987, by The American College of Obstetricians and Gynecologists.