The precision and reliability of the stable microbubble test as a predictor of respiratory distress syndrome (RDS) were studied. In blind experiments, the stable microbubble test was performed by three analysts in quadruplicate on six different amniotic fluid samples obtained from pregnant women whose babies developed RDS and on three samples prepared from mature controls. Three‐way analysis of variance revealed that there were statistically significant differential effects of the analyst, observer, and sampling on the stable microbubble values, and also that there were statistically significant interactions between the analyst and observer as well as between the analyst and sampling. However, the magnitude of these effects was not large enough to modify the interpretation of the test results. We conclude that the rapidity, simplicity and reliability of the stable microbubble test allow for its use as a bedside procedure in identifying infants who are likely to develop RD