Arginine vasopressin (AVP) or its V1 receptor antagonist d(CH2)5Tyr(Me)AVP was administered directly into the septal brain area of adult male rats by means of inverse microdialysis. Immediately after a 30-min dialysis period, during which either approximately 0.25 ng AVP or 5 ng of the V1 antagonist were delivered into the brain tissue, anxiety-related behaviour of the animals was measured on an elevated plus-maze apparatus. While synthetic AVP failed to alter plus-maze behaviour compared to vehicle-treated controls, animals treated with the V1 receptor antagonist made more entries into (P < 0.01) and spent more time on the open arms (P < 0.05), indicating reduced anxiety. Since administration of neither AVP nor the V1 antagonist significantly influenced general locomotor activity of the rats on the plus-maze and in an open field, these data point towards a critical involvement of intraseptally released AVP in the emotional evaluation of novel situations.