Fetal adrenal function during pregnancy has a probable role in parturition. Ninety-five mothers and fetuses were evaluated to ascertain maternal or fetal plasma cortisol interrelationships under various clinical situations. When mode of delivery was evaluated, maternal cortisol levels showed no differences. However, the fetuses from vaginal delivery (mean, 43.7 mug/100 ml) had higher levels than those from cesarean section (mean, 34.7 mug/100 ml). Induction of labor showed a rise in maternal cortisol from preinduction levels (mean, 40.2 mug/100 ml) to delivery (mean, 49.6 mug/100 ml), probably reflecting the maternal stress of labor. The fetal cortisol level after induced labor (mean, 35.2 mug/ml) supporting the adrenal contribution to the initiation of labor. Gestational age of the fetus was significant in the fetal cortisol levels: 36 weeks or less (mean, 34.1 mug/100 ml); 37 weeks or more (mean, 44.5 mug/100 ml). This again supports the development of adrenal maturity. Fetal weight, postdatism, acute and chronic fetal distress, hypertensive disease in pregnancy, and race were evaluated without revealing any significant intergroup differences. Two anencephalic pregnancies were also studied.