Studies of gamma-globulin on 16 infants at ages 3 days, 1, 2, and 3 months show a drop in concentration which results primarily from dilution in an expanding plasma volume. The total circulating gamma-globulin remains relatively constant from age 3 days through the first 3 months of life. As degradation of protein is probably taking place, it is concluded that the normal loss is being replaced by synthesis by the infant.