Serum ceruloplasmin activity in full term and premature neonates was measured on the first day of life. Preterm newborns were born more than 24 hours after antenatal corticosteroid treatment, had enzyme activity equivalent to that of the full term babies. Little or no ceruloplasmin activity was found in those prematures who were born without steroid prophylaxis. Highly significant correlation was observed between the initial ceruloplasmin activity and the morbidity and mortality of respiratory distress syndrome.