Amniotic fluid samples for physiologic maturity tests are frequently (15 to 20%) contaminated with blood and/or meconium. The effects of this contamination on the lecithin/sphingomyelin ratio is well known. However, less is known about the effect of blood and meconium on the rapid surfactant test. Additionally, because the RST may be performed in the office or at bedside, there is the possibility of temperature affecting the result. Therefore, the effects of blood, meconium, and temperature on the rapid surfactant test have been investigated. Contamination with blood or meconium may result in a false indication of fetal maturity. However, the test may still provide useful information concerning pulmonary status of the fetus, if the rapid surfactant test is intermediate or immature despite contamination. Temperature also affects the reliability of the rapid surfactant test. The test is found to be most reliable in the range of 20 to 30 C (with higher temperatures the bubbles dissipate more rapidly; with lower temperatures the foam is more stable).