FUKAYA, T., FURUHASHI, N., SHINKAWA, O., KONO, H., TAKAHASHI, T. and SUZUKI, M. The Human Fetal Prolactin and Estradiol Levels, and Their Correlationship. Tohoku J. exp. Med., 1984, 143 (1), 87-92-Serum prolactin and estradiol-17β levels were determined in umbilical cord sera obtained from 33 preterm, 118 full-term and 11 anencephalic infants and in peripheral sera obtained from 5 neonates. Prolactin levels increased from mid-gestation toward term, and markedly decreased after birth. Those in anencephalic infants (253±86ng/ml, mean±S.D.) were lower than in full-term infants (324±119ng/ml), but the difference was not statistically significant. We also performed thyroid-releasing-hormone (TRH) (50-200μg) test on 5 anencephalic infants, but significant changes of serum prolactin levels were not found. Estradiol-17β levels in anencephalic infants were significantly lower than those in full-term infants. There was a significant positive correlation between cord prolactin and estradiol-17β levels in full-term infants. These results suggest one of the control factors for human fetal pituitary prolactin secretion is estrogen, and hypothalamic factors are not so important.-prolactin; estradiol; TRH; fetus