Massive bleeding during pregnancy has a significant effect on the mother and the fetus. To evaluate the safety of hemodilution as a therapy for hemorrhage during pregnancy, the author compared maternal and fetal hemodynamics and oxygen carrying capacity at varying conditions in gravid ewes. Six Corriedale-breed, near-term pregnant ewes (120-140 days gestation) were anesthetized with nitrous oxide, halothane and oxygen. After the vital signs became stable, the maternal and fetal parameters of hemodynamics and oxygen carrying capacity were measured as control values. After then, 15% of total estimated matemal blood volume (12.5 ml/kg) was removed over approximately 15 minutes and infusion of the same amount of a mixture of lactated Ringer's solution and 10% pentastarch was done simultaneously (15% bleeding). Twenty minutes later the same parameters were measured. After then, a second phlebotomy was performed to remove an additional 15% of the total estimated maternal blood volume and infusion of the same amount of a mixture of the same solutions was done simultaneously (30% bleeding). And the same parameters were measured. Data collections included matemal heart rate, systolic, diastolic and mean arterial pressure, central venous pressure, pulmonary artery pressure, pulmonary capillary wedge pressure, cardiac output, hemoglobin, hematocrit, serum lactate, arterial and mixed venous pH, oxygen tension, carbon dioxide tension, oxygen saturation, and fetal heart rate, systolic, diastolic and mean arterial pressure, hemoglobin, hematocrit, serum lactate, and umbilical arterial and venous blood gas analysis. Matemal arterial blood pressure, heart rate, central venous pressure, pulmonary artery pressure, pulmonary capillary wedge pressure and carfiac output revealed no significant changes, and there was neither hypoxemia nor acidosis in gravid ewes. Serum lactate concentration at 30% bleeding increased significantly but within normal range. Oxygen flux, oxygen consumption and oxygen extraction ratio revealed no significant differences. In fetal lamb blood pressure was not changed, but heart rate, serum lactate concentration and oxygen extraction ratio were revealed significant increases in 15% bleeding and 30% bleeding cases. In conclusion, gravid ewe was well tolerated to acute hemodilution, and.fetal lamb was well compensated.