A deficit of lung surfactant is known to be involved in the pathophysiology of the respiratory distress syndrome of the neonate (RDS), which is still responsible of about one fourth of total neonatal mortality. It has been well documented that maternal administration of corticosteroids enhances fetal lung maturity, promoting synthesis of surfactants and altering also the structure of the lung parenchyma. Although the beneficial effects of corticosteroids have been substantiated by a number of experimental evidences and clinical studies, about 10% of the treated neonates remains affected by RDS. Corticosteroids affect the composition of lung parenchyma, by increasing elastin content and by decreasing alveolo-capillary permeability to serum proteins. Since thyrotropic releasing hormone (TRH) has been shown to potentiate the effects of corticosteroids a combination of the two drugs may be the treatment of choice for prenatal prevention of RDS.