In this review we present data summarizing our studies concerning the mechanism of action for the behavioral effects of peripheral arginine vasopressin (AVP) administration. We have demonstrated a clear performance improvement in a one trial appetitive task designed to measure the memory-learning process. This behavioral effect is blocked by peptide analogs which block the pressor response to AVP. From these data, and from other data obtained in aversively motivated tasks, we hypothesize that peripheral AVP injections induce effects of physiological-endocrinological origin and that these peripheral signals (e.g. vasopressor actions) alert and arouse the animal, thus helping to improve its association of environmental events. This hypothesis is similar to that proposed by others regarding peripheral hormones and memory and still leaves open the possibility that vasopressin in the brain acts independently of the above proposed action for peripherally derived vasopressin.