DHA-S loading has been widely used for the assessment of placental function and ripening of the cervix before delivery. However, changes in the steroidal milieu in both mother and fetus has not been clarified after DHA-S administration. Free (f) and conjugated (c) DHA, delta 5 androstenediol (Adiol), estradiol (E2), estriol (E3), f-testosterone (T) and delta 4 androstenedione (Adione) levels in maternal vein, cord blood and peripheral vein of new born infants after maternal DHA-S administration were measured by radioimmunoassay, and the levels were compared to those in the controls. DHA-S administration resulted in a marked and significant rise in all steroid levels except for E3 in maternal vein. Significant augmentation of T, Adione, c-Adiol, f-DHA, f.c-E2 in umbilical artery, and T, Adione, f.c-Adiol, f-DHA, f-E2 in umbilical vein was observed. Steroid levels during the neonatal period were also measured on the 1st, 3rd and 5th days in both male and female infants, and the levels were compared to those of the controls. Although three androgens in both male and female infants at delivery were significantly higher than the controls, no significant difference was observed on the 5th day of life. Adiol and Adione levels on the 1st day in females, and Adiol levels on the 3rd day in males were higher than those of the controls. E2 levels remained high till the 5th day of life. These results indicated that DHA-S administered to the mother was converted to androgen and estrogen promptly in the placenta and transferred to the fetus.(ABSTRACT TRUNCATED AT 250 WORDS)