The changes in blood levels of prolactin, total and free cortisol, and cortisone were studied and compared in 51 mother-infant pairs, 30 with eutocic delivery and 21 with dystocic delivery. Regardless of the type of delivery, the newborn at term showed significantly higher prolactin and cortisone serum levels than their mothers, and significantly lower levels of free and total cortisol. In fetal distress of short duration, free cortisol levels were significantly raised in both the mother and the child, while prolactin and cortisone levels were significantly higher only in the child. In contrast to these observations, serum prolactin and cortisone levels in the mother were not altered by the occurrence of fetal distress. In the newborn at delivery there was a negative correlation between serum prolactin and the Apgar score at 1 min applied to the part of the graph between 8 and 2 Apgar scores. This study illustrates the utility of fetal prolactin measurements in evaluating the stress to which the fetus is subjected.