Destructive changes have been described by others in the respiratory bronchioles, alveolar ducts, and alveoli associated with hyaline membranes in the lungs of infants who died in the first few hours of life. After 24 hours of extra-uterine life, cellular proliferative phenomena appear in these same areas and are almost always present after 48 hours of extra-uterine life. It is suggested that these represent a reparative process related to the early destructive changes associated with the formation of the hyaline membrane, rather than a purely reactive phenomenon associated with the formation of phagocytes involved in the removal of the membranes.