Amniotic fluid was obtained from 85 women during the last trimester of gastation and analyzed for cortisol by a radioimmunoassay procedure and for lecithin/sphingomyelin (L/S) ratios by a combined thin-layer chromatography densitometer scanning technique. A total of 114 samples were examined. Cortisol values ranged from 38 to 438 ng. per milliliter; L/S ratios ranged from 0.3 to 9.2. Comparison of cortisol levels with L/S ratios by multiple regression analysis gave an "r" value of 0.371. From less than 32 weeks' gestation to 41 or 42 weeks there was an increase in cortisol levels from 139 plus or minus 124 to 290 plus or minus 78 ng. per milliliter whereas the L/S ratios increased from 1.8 plus or minus 2.3 to 3.9 plus or minus 2.0. These data indicate that there is no good correlation between cortisol and L/S ratios in the samples of amniotic fluid analyzed.