The plasma concentrations of the gastrointestinal regulatory peptides vasoactive intestinal polypeptide (VIP), insulin, secretin, somatostatin, motilin, pancreatic polypeptide (PP) and gastric inhibitory polypeptide (GIP), as well as blood glucose, were measured in eight healthy women before, during and after oxytocin infusion in post-term pregnancies. Plasma VIP increased significantly (P less than 0.01) during oxytocin infusion. Plasma secretin showed a significant (P less than 0.05) decrease during oxytocin infusion. Plasma somatostatin remained unchanged during oxytocin infusion, but thereafter a significant (P less than 0.05) increase occurred. Both plasma motilin and plasma PP showed a non-significant increase during oxytocin infusion with sustained levels thereafter. No changes were found for plasma insulin, GIP and blood glucose.