Changes in hemodynamics and blood components were studied in newly born pigs bled one-third of their measured blood volume. Decrease in heart rate accompanied the significant drop in arterial and central venous pressures after blood loss. The recovery of heart rate, arterial and venous pressures from hemorrhage during the 24 h that followed and the concomitant decrease in the hematocrit indicated that recovery was due to the replenishment of plasma volume. The pattern of plasma volume restoration was similar to that of the adult man and adult animal except that it occurred at a much faster rate with a tendency to overcompensate. The restoration of the total amount of circulating plasma proteins was completed within 14 h of the initiation of hemorrhage. The rapid influx of proteins into the circulation was primarily due to the albumin, alpha-globulin and fibrinogen fractions. The highly significant increase in the circulating reticulocytes that took place from the 12- to 24-hour period after blood loss suggests a large increase in erythropoietic activity. Data obtained from this study support the concept that the cardiovascular regulatory system is, at birth, different from the adult. They also indicate that, at least, some of the homeostatic processes involved in the restoration of blood volume and plasma proteins are functional in the neonate.