Evidence was obtained with a highly purified prepn. that vasopressin, in addition to its pressor and antidiuretic activities, possesses intrinsic oxytocic action as one of its pharmacological properties, in contrast with purified oxytocin which appears not to possess pressor or antidiuretic activity. For each 100 units of vasopressor-antidiuretic activity there is intrinsic "oxytocic" activity represented by approx. 5 units as determined by the isolated rat uterus assay or by approx. 13-15 units by the chicken blood pressure depressor assay. The evidence that vasopressin possesses milk-ejection activity about 1/5 that of oxytocin was discussed.