An analysis of the blood of 20 women revealed the existence of an anemia during preg-nancy. Simultaneously there was found to occur with the advancement of pregnancy an increase in the water content of the blood and a fall in cell volume and re-fractive index. The maximum deviations from the nor-mal in Hb and blood solids occured at 220 days. The cell volume, sedimentation index, and refractive index underwent approximately concurrent changes. Since the character of these changes is similar to that previously obtained with the pregnant rat, it is considered possible that the hydremic condition might occur in other preg-nant animals as well. However, observations on 40 cows selected for high milk production did not reveal either an anemia or a hydremic state.