Total and intrarenal distribution of blood flow was determined repeatedly in five unanesthetized dogs using the 85Kr method. No consistent effect of oxytocin (syntocinon) could be demonstrated. Eleven anesthetized dogs showed similar TRBF variability. However, intravascular silicone rubber injections and autoradiographs suggest a postglomerular (vasa rectae) dilation in response to oxytocin. Water intoxication occurs in dogs given massive doses of oxytocin with a water load as is seen in man. Kidneys from pregnant, postpartum and suckling bitches show the similar vasa rectae dilation to that induced with oxytocin. Progesterone also appears to have some effect. Estrogen and oxytocin appears to interact diminishing cortical flow with little effect on the vasa rectae. No interaction of oxytocin and autonomic blocking agents, prostaglandin A1 or F2a or chorionic gonadotropins was demonstrated.