Some renal parameters have been studied in newborns with respiratory distress syndrome (RDS). During the first 24 h, the serum creatinine level of the severe cases of RDS are significantly increased, decreasing gradually with improvement of the RDS and reaching normal values within 10 days. Blood urea nitrogen remained unchanged. In the milder cases of RDS, the serum creatinine also showed a slighter increase, which became normal within 4 days after birth. During the acute phase of RDS, there is a reversible impairment in the renal function, which correlates with the degree of hypoxia, hypercapnia and acidosis determined by the primary disease.