The origin of human placental oxytocinase.

1. Placentas from normal women and from those with pre-eclamptic toxaemia, taken immediately after labour, were examined for oxytocinase activity and analysed morphometrically.2. Both enzyme activity and volume of syncytiotrophoblast were significantly reduced in placentas from patients with toxaemia.3. There was a positive correlation between the enzyme activity and the proportion of trophoblast in the placenta. When the activity was expressed per unit volume trophoblast, there was very little difference between placentas, whether from normal subjects or from patients with toxaemia.4. It is concluded that human placental oxytocinase is located in the syncytiotrophoblast.