Our aim was to confirm the role of postganglionic vagal fibres and vasoactive intestinal polypeptide (VIP) in mediating the vagal tachycardia in anaesthetised dogs. Vagal postganglionic stimulation after atenolol (1 mg/kg) and hexamethonium (10 mg/kg) caused a bradycardia (40 beats/min, n = 2), after atropine (0.5 mg/kg i.v.) the resulting tachycardia (37 beats/min) was attenuated by VIP receptor antagonism with VIP (6-28) (100 mu g i.c.) by approximately 50%. VIP release from vagal postganglionic fibres mediates the vagal tachycardia.