Arginine vasopressin is reported to have an excitatory effect on hippocampal neurons in the slice preparation. However, vasopressin also has a classic vasopressor action on mammalian blood vessels. We used the rat hippocampal slice to examine the effects of this peptide on central neural and vascular targets. The hippocampus is densely vascularized and pyramidal cells are enmeshed in a network of microvessels. Vasopressin increased the excitability of impaled neurons without substantially altering membrane potential or resistance. The peptide also caused pronounced vasoconstriction in penetrating microvessels when applied at micromolar concentrations. The concerted action of vasopressin on neurons and blood vessels and the physical proximity of these cell types suggest mechanisms whereby these responses may be associated.