Rats injected with arginine vasopressin (AVP) immediately after exposure to a novel open-field environment found a water tube faster than saline injected rats, when water-deprived 48 h later. Other experiments demonstrated that this effect did not result from some conditioned or pharmacologically-induced hyperactivity in the experimental group. Although these results are consistent with a role for AVP in 'memory' mechanisms, lithium chloride, a known illness-producing agent, produced a reduction in latency to find the water tube identical to that of AVP. In separate experiments, AVP acted as an effective unconditioned stimulus in conditioned taste and place aversion studies. AVP also produced a dose-dependent disruption of spontaneous locomotor activity. Together, these data indicate that peripheral AVP administration has aversive consequences. Desglycinamide arginine vasopressin (an AVP analog with weak pressor-agonist properties) produced no observable aversive effects and did not improve test performance in the appetitive water-finding task. It is suggested that the apparent memory-enhancing properties of peripherally administered AVP, at least in appetitive test paradigms, may depend on its aversive and consequently arousing actions.