To predict the development of respiratory distress syndrome (RDS) in premature neonates who might benefit from early administration of surfactant, the clinical applicability of stable microbubble (SM) test was prospectively evaluated. Fifty-nine preterm neonates with the gestational ages of less than 37 weeks were studied. SM test was performed on gastric aspirates obtained within 30 minutes after birth. The number of microbubbles was correlated with later development of RDS. With a cut-off value of less than 10 microbubbles/mm2, the SM test showed a positive predictive value of 76.0% (19/25) and a negative predictive value of 97.1% (33/34), while sensitivity and specificity were 95.0% (19/20) and 84.6% (33/39), respectively. The overall accuracy was 88.1% (52/59). It was concluded that use of the SM test on gastric aspirates immediately after birth is a rapid, simple and reliable procedure for identifying those neonates with surfactant deficiency who may benefit from prophylactic surfactant therapy.