Cholesterol esterification was studied in adult and cord serum by measureing the initial rate of lecithin-cholesterol acyl transferase (LCAT) activity. Cord serum had about one-third as much free and esterified cholesterol and about one-half as much LCAT as adult serum. When the adult LCAT activities are plotted against the individual's serum free cholesterol levels a straight line relationship results (0.101±.005% cholesterol esterified per min). Cord serum LCAT activities (.135±.0407% cholesterol esterified per min) in the main fall above the adult line. Our results show that cord serum can esterify cholesterol at a rate equal to or higher than adult serum when the LCAT activity is related to the amount of serum free cholesterol present.