In human placenta, lack of autonomic innervation suggests that vascular tone is controlled by humoral factors such as thromboxane. A recent study on vasoconstriction to a thromboxane mimetic, U46619, in chorionic plate arteries from pregnancies with maternal obesity, showed that responses were unaltered1. The effect of gestational diabetes (GDM) on the contractile response of chorionic vessels to U46619 is not known. Since functional studies on fresh placental tissue can be challenging because of the unpredictability of placenta availability, responses were investigated in both fresh vessels and after overnight storage. Human placentas from normal (n=7) and GDM (n=3) pregnancies were collected following elective caesarean sections at term. Segments of chorionic arteries and veins were dissected and divided into two: (a) fresh and (b) overnight-stored (physiologic salt solution2 with 2% Ficoll and 5% CO2 in air gassing, 4○C). Responses of the vessel segments to U46619 were investigated by isometric tension recording3. Cumulative responses to U46619 were expressed as a percentage of the contractile response to KCl (60 mM). Data were analysed using two-way ANOVA. U46619 (1 nM – 30 µM) elicited concentration-dependent contractions in the chorionic arteries and veins. Contractile responses to U46619 were similar between GDM and normal groups in both arteries and veins (P>0.05). After overnight storage, contractile responses to U46619 were also similar between GDM and normal groups, in both arteries and veins (P>0.05), suggesting a stable agonist response that can be studied after overnight storage. Contractile responses to U46619 are unchanged in chorionic arteries and veins from GDM pregnancies, as in chorionic arteries from pregnancies with maternal obesity.