Background: Respiratory distress is one of the most common causes for admission in NICU. Respiratory distress syndrome is a common cause for respiratory distress especially in the newborn while transient tachypnea of newborn TTN is a common cause in fullterm infants especially who delivered by caesarean section.
Aim of the work: to assess the value of lactate dehydrogenase serum levels on differentiating between RDS and TTN in Neonates suffering from respiratory distress.
Methods: The study is a cross sectional study conducted on 90 neonates delivered by cesarean section and suffering from respiratory distress recruited from neonatal intensive care unit during the period from April 2023 to November 2023. They were classified into two groups: group I:  included 45 neonates who suffered from RDS and group II: included 45 neonates who suffered from TTN diagnosed clinically and radiologically. In addition to history taking and clinical examination and chest x-ray; the following laboratory investigations were done: Serum lactate dehydrogenase level, complete Blood Count (CBC), CRP and ABG.
Results: Our results showed that serum LDH level is significantly higher (p value=0.001) in RDS neonates (mean= 1040±110 in 1^st day and 1482 ±170 in the 3^rd day) than in TTN neonates (mean=898±90.6 in 1^st day and 709±211 in the 3^rd day).
Conclusion: Lactate dehydrogenase (LDH) serum levels can differentiate between respiratory distress syndrome and transient tachypnea of newborn in neonates. LDH levels were higher in neonates suffering from RDS