OBJECTIVE Failure of adequate and timely clearance of fetal lung fluid has been implicated in transient tachypnea of the newborn (TTN). There has been lack of human data on the association between endocrinological adaptation and fetal lung fluid clearance. Although TTN development in term or late preterm newborns delivered by cesarean section (CS) is well known, whether stress hormones levels at birth contribute to it or not is not known. The aim of the study was to assess the possible association between low adrenocorticothrophic hormone (ACTH), cortisol and free triiodothyronin (fT3) levels at birth and TTN in late preterm and term infants. STUDY DESIGN We compared cord blood concentrations of epinephrine, cortisol, ACTH, fT4, fT3 and thyroid stimulating hormone in two groups of term and late pretrem infants born by CS: those who developed TTN and a comparison group without respiratory distress. RESULTS While there were no significant demographic differences between patient and control groups, cord ACTH, cortisol and fT3 were significantly lower and epinephrine was higher in infants developing TTN (p < 0.05). CONCLUSIONS Lower cord levels of cortisol, ACTH and fT3 in patients with TTN may indicate the possible relation of these hormones in fetal lung fluid clearance and postnatal pulmonary adaptation through their modulatory effect on epithelial sodium channel and Na-K-ATPase.