Clinical and radiological classifications of the severity of the respiratory distress syndrome (RDS) were made in 55 infants. According to the clinical classification 17 infants belonged to the first class (mild RDS), 22 to the second (moderate RDS), and 16 to the third class (severe RDS). In the classification based on radiological findings the numbers of infants in classes 1, 2 and 3 were 18, 19 and 18 respectively. On the basis of both the clinical and radiological findings, 11 infants belonged to the mild RDS class, 11 to the moderate, and 12 to the severe RDS class. Thus, 34 infants had the same clinical and radiological classification. In 21 infants there were discrepancies between the clinical and the radiological classifications, but only one infant with the most severe radiological findings belonged to the mild RDS class and only one infant with mild radiological findings belonged to the worst RDS class.