Serial blood volume measurements were made in 27 normal full-term newborn infants using iodinated human albumin. At the moment of birth the newborn infant was estimated to have a blood volume of 78 ml/kg with a venous hematocrit of 48 %. When the cord-clamping was delayed for 5 minutes the blood volume increased by 61 % to 126 ml/kg. This placental transfusion amounted to 166 ml for a 3500 g infant, one-quarter of which occurred in the first 15 seconds, and one-half within 60 seconds of birth. Stripping of the umbilical cord 10 times during the 5 minutes did not increase the volume of the transfusion.

When the placental transfusion was prevented by immediate clamping of the cord, the blood volume did not change appreciably during the first 4 hours of life. On the other hand, there was a marked decrease in blood volume from 126 to 89 ml/kg during the first 4 hours in infants who had received a placental transfusion. This decrease was brought about by the transudation of one-half of the original plasma volume, so that the venous hematocrit rose from 48 % at birth to 64 % by 4 hours.

In all but three of the infants studied there was an increase in blood volume between 4 and 24 hours of age which was due to an increase in plasma volume averaging 22 ml per infant. There was no appreciable change in blood volume between 24 and 72 hours of age.

The red cell volume remained stable during the first three days of life in each of the infants; those who had received a placental transfusion maintained a red cell volume about 60 % larger than those who had not.

At 72 hours of age the blood volume had stabilized after the plasma shifts of the first day of life, and the range of values extended from 75 to 107 ml/kg. This variation between individuals was due in large part to differences in hematocrit which ranged from 39 % to 67 %, and these in turn were related to the volume of placental transfusion.

Average values at 72 hours for infants who had received no placental transfusion were 82 ml/kg blood volume, 31 ml/kg red blood cell volume, 51 ml/kg plasma volume, and 44 % venous hematocrit. For infants who had received a placental transfusion they were 93 ml/kg blood volume, 49 ml/kg red blood cell volume, 44 ml/kg plasma volume, and 60 % venous hematocrit.