Free estradiol and estriol was determined radioimmunologically in cord blood and in peripheral venous blood during the third, fifth and seventh day of life. The steroid level of a group of children with icterus neonatorum simplex were compared with an anicteric control group. In spite of the higher level of estriol in cord blood during the first week of life, estriol was eliminated much more rapidly than estradiol and independent of the bilirubin level. Given the same initial values for estradiol in cord blood of both control groups, the estradiol elimination rate was significantly slower in icteric newborns. The level of estradiol in cord blood was significantly higher in newborn males than in newborn females. A higher level in cord blood, however, does not increase the risk of a later newborn hyperbilirubinemia. Our findings tend to indicate that no etiologic importance should be attached to the amount of estradiol and estradiol to be eliminated, for the development of icterus neonatorum simplex. At the same time, icteric newborns have a relative insufficiency in estradiol elimination but not, however, in estriol elimination.