Previously, we have demonstrated that forced swimming triggers the release of arginine vasopressin (AVP) within the septum of rats, where AVP modulates stress-coping strategies. The present study was designed to examine the effects of forced swimming on the release of AVP within the amygdala. Therefore, adult male Wistar rats were chronically implanted with a microdialysis probe aimed at the amygdala to monitor the local release of AVP under both resting and stress conditions. A 10-min forced swimming session caused a significant increase in the extracellular AVP concentration (to 366 +/- 90% of baseline; P < 0.05) within this brain area. In a subsequent experiment we investigated the physiological impact of the stressor-induced release of AVP by administrating the AVP V1 receptor antagonist d(CH2)5Tyr(Me)AVP into the amygdala via inverse microdialysis. Bilateral antagonist treatment modulated the behavioural response acutely by increasing the time the animals spent struggling and by reducing the time the animals floated. Our results demonstrate a significant activation of the vasopressinergic system within the amygdala in response to forced swimming. AVP released within the amygdala seems to be involved in the generation of passive coping strategies in stressful situations. Taken together with previous findings the results of the present study suggest that AVP is released within septum and amygdala to balance the behavioural response during forced swimming.