L-371,257 is a compound used in scientific research which acts as a selective antagonist of the oxytocin receptor with over 800x selectivity over the related vasopressin receptors.[1] It was one of the first non-peptide oxytocin antagonists developed,[2][3][4][5] and has good oral bioavailability, but poor penetration of the blood–brain barrier which gives it good peripheral selectivity with few central side effects.[6] Potential applications are likely to be in the treatment of premature labour.[7]