DGAVP facilitates consolidation and retrieval of active and passive avoidance behavior. In this study it was tested whether the long-term behavioral effects of DGAVP are the consequence of an initial increase in behavioral arousal during the learning phase. Animals that were preestimated in an open field test to be low active showed a lower number of conditioned avoidance responses (CAR's) during acquisition and extinction of a shuttle-box task than high active rats. DGAVP was administered 40 min prior to the 1st acquisition session. The immediate effect of DGAVP was a shift in the bell-shaped curve of the relation between arousal and performance (13); an increase in acquisition performance was observed with a low dose of DGAVP (0.1 microgram), while a decrease was found with a high dose of DGAVP (1 microgram). A dose-dependent inhibition of extinction was found in both low and high active animals. These results suggest an immediate effect of DGAVP on the rate of acquisition behavior, which may be a direct consequence of its arousing properties, and a long-term effect on extinction, indicating the formation of memory traces specific for vasopressin-related neuropeptides.