Catheters were implanted into the fetal dorsalis pedis and maternal jugular veins of 6 ewes of 122–130 days gestation age. Fetal plasma arginine vasopressin (AVP) concentrations rose in the last few days before parturition from undetectable levels to values associated with response to minor stress. Similarly, AVP was frequently present in maternal plasma in the last week of gestation but was rarely detected earlier. The levels attained in the mother were somewhat lower than in the fetus.