Cholic and chenodeoxycholic acids were determined in 42 cord plasma samples after pregnancies complicated by maternal intrahepatic cholestasis and in 20 cord plasma samples after uncomplicated pregnancies with a gas-chromatographic method. The mean total amount of these bile acids was 1.8 mug per milliliter after uncomplicated pregnancies as compared to 5.6 mug per milliliter (P less than 0.001) in the cholestasis group. These bile acids were also determined in six maternal plasma samples where, as compared to the cord plasma of their babies, higher levels were found in every case. These results show that in addition to changes in the maternal circulation, maternal cholestasis elevates bile acid levels in fetal circulation. A more frequent occurrence of signs of fetal distress during pregnancy or labor was found in those cholestasis cases where cord plasma bile acid levels were high. The relationship of fetal bile acid levels to fetal steroid hormone metabolism was studied by correlating total bile acid levels with the concentrations of a number of steroid sulfates in cord plasma. An interesting finding was a negative correlation between fetal bile acid levels and concentrations of 16-oxygenated steroid sulfates, which are important estriol precursors produced by the fetus. These observations led to the conclusion that bile acids or other substances which are retained in maternal circulation as a result of cholestasis may, after transplacental passage, cause some kind of distress to the fetus.