Since vasopressin and oxytocin might be involved in processes of storage and retrieval of information in rats, the distribution of these hormones within the central nervous system was measured employing sensitive and specific radioimmunoassays in combination with an extraction method using Vycor glass powder. Vasopressin was detected in hypothalamus, amygdala, septum, hippocampus, nucleus parafascicularis and medulla oblongata of Wistar and Brattleboro rats, heterozygous for diabetes insipidus. It was not detectable in samples of Brattleboro rats, homozygous for diabetes insipidus. Oxytocin was found in hypothalamus, septum and nucleus parafascicularis of Wistar rats in lower amounts than vasopressin while it was present in higher amounts in the medulla oblongata. The extensive distribution of these hormones in the rat brain suggests a possible role in a variety of central nervous system processes rather than solely in the expression of acquired behavior.