The results are presented of fluorescence polarization as a method for measurement of surfactant production in 159 specimens of amniotic fluid collected from pregnant women with diabetes, hypertension, Rh immunization, premature rupture of membranes (for more than 48 h prior to delivery) and intrauterine growth retardation (IUGR). The predictability of the development of respiratory distress syndrome has been assessed by this assay. Its specificity, sensitivity and overall accuracy were similar to the lecithin/sphingomyelin (L/S) ratio. The influence of the conditions detailed on fetal lung maturation was determined, lung development being enhanced until near term by Rh immunization, rupture of membranes and hypertension with IUGR.