(d(CH2)51,Tyr(Me)2,Orn8)-Oxytocin is a potent oxytocin antagonist with a pA2 of 7.35?0.08. It has been used to support the hypothesis that pituitary secretion of oxytocin is associated with coactivation of centrally projecting brain oxytocin pathways, some of which are causally associated with induced inhibition of food intake. In addition, it competitively inhibits the contraction of arginine vasotocin (AVT) without affecting the efficacy of AVT.