OBJECTIVE To evaluate the reliability of the dipalmitoyl phosphatidylcholine test in predicting respiratory distress syndrome (RDS) in the presence of common contaminants of amniotic fluid. METHODS Forty specimens of amniotic fluid collected within 72 hours of delivery were divided in five 25 microL aliquots and diluted with either phosphate-buffered saline (control), meconium, blood, vaginal fluid, or semen. The concentration of dipalmitoyl phosphatidylcholine in all five groups of samples, as measured by the dipalmitoyl phosphatidylcholine test, was compared by paired t test, Dunnett test, and analysis of variance, and correlated with the neonatal respiratory status of the newborns. RESULTS No significant differences in the concentration of dipalmitoyl phosphatidylcholine were found between control and the corresponding contaminated samples (P = .33). Of the 200 samples evaluated, 80 had dipalmitoyl phosphatidylcholine concentrations below 12 micrograms/mL and 120 had at least 12 micrograms/mL. Using a cutoff dipalmitoyl phosphatidylcholine concentration of 12 micrograms/mL, the presence of RDS was predicted accurately in all 15 control and in 61 of 65 contaminated samples. The absence of RDS, as predicted by a dipalmitoyl phosphatidylcholine value at least 12 micrograms/mL, was predicted accurately in 24 of 25 control samples and 96 of 100 contaminated samples. The overall accuracy of the dipalmitoyl phosphatidylcholine test in predicting RDS in contaminated samples was 98%. CONCLUSIONS The dipalmitoyl phosphatidylcholine test is a reliable predictor of RDS in contaminated samples.