A rapid, simple inexpensive test has been devised to determine whether pulmonary surface-active material (surfactant) is present in amniotic fluid. The test depends on the ability of the pulmonary surfactant to generate stable foam in the presence of ethanol. Analysis of 138 samples of amniotic fluid showed that an appreciable titer of the surfactant appears on the average at 33 weeks' estimated gestation but that the time of appearance is variable from 25 weeks to term. When test results were sorted into three zones (clearly negative, intermediate, and clearly positive) infants of 12 of 12 patients with clearly negative tests had severe respiratory-distress syndrome or transitional respiratory distress, whereas those of 68 of 68 patients with clearly positive tests were free of respiratory distress. In 13 cases with intermediate tests eight of the infants showed mild to severe respiratory difficulty. The test has high predictive value for respiratory-distress syndrome when applied to uncontaminated amniotic fluid.