The developmental metabolism of bile acids can be partly studied by the analysis of bile acid patterns in meconium. Employing modern analytical techniques, it has been found that besides the main bile acids of humans (cholic, chenodexoycholic, deoxycholic, and lithocholic acids) several "atypical" bile acids occur in meconium. It is unlikely that these "atypical+ bile acids are derived from materno--fetal transfer, and they therefore probably reflect a special fetal bile acid metabolism. Hydroxylations at positions 1 and 6 of the steroid skeleton are regularly encountered. These hydroxylations, as well as the occurrence of 3 beta-hydroxy-delta 5 compounds and of bile acids of the 5 alpha series, suggest that fetal bile acid synthesis differs markedly from that of the adult. These observations are of interest in relation to the origin of unusual bile acids found in the cholestatic condition of the adult. It appears that a resurgence of the fetal biosynthetic patterns takes place under the conditions of cholestatic liver disease.