To predict the development of respiratory distress syndrome (RDS), the authors determined the fluorescent polarization values on gastric aspirates obtained from 67 premature infants within 30 minutes of birth. In 29 cases these results were also compared with the fluorescent polarization values measured on the corresponding amniotic fluid samples. Measurements for microviscosity were made by fetal lung maturity analyzer. Among 15 of 67 premature infants who developed RDS, the fluorescent value measured on gastric aspirates in all 15 infants was greater than 0.320. The fluorescent polarization values were less than 0.320 in all 52 infants in whom RDS did not develop, a predictability of 100%. Direct comparison found fluorescent polarization values measured on gastric aspirates to be somewhat lower than the corresponding amniotic fluid fluorescent polarization values. The results indicate that gastric aspirate obtained within 30 minutes of birth contains swallowed amniotic fluid. In cases where amniotic fluid samples were not available for surfactant evaluation prenatally, the determination of fluorescent polarization values on the newborn's gastric aspirate may accurately predict the development of RDS. The use of the fetal lung maturity analyzer microviscosimeter provides a simple, reliable, and rapid (45 minutes) method for assessment of surfactant in premature infants.