For predicting the risk of respiratory distress syndrome (RDS), lung surfactant in amniotic fluid can be assessed by observation of stable microbubbles (<15 µm diameter). It was investigated if the stable microbubble test (MT) developed on amniotic fluid could be applied on tracheal aspirate samples (TA) obtained from newborn infants. Forty-four TA from 29 newborn infants without pulmonary diseases (group 1) and 65 TA from 21 newborn infants with respiratory insufficiency (group 2) were analyzed by the MT for predicting surfactant deficiency and/or surfactant malfunction. Ten microbubbles/mm2 was defined as cutoff value of the MT. A specificity of 90% and a sensitivity of 52% was obtained with this cutoff value. A much lower rate of false negative results (sensitivity 91%) was noted after surface tension measurement of TA. The sensitivity of the MT (52%) does not encourage the use of the MT on TA.