Experiments were performed in anaesthetized dogs to find out whether the response of decreases in vagus nerve activity to distension of the urinary bladder is affected by changes in carotid sinus pressure. The carotid sinuses were vascularly isolated and perfused with blood at constant flow. Both ureters were cannulated and the urinary bladder was distended with warm Ringer solution. In eight dogs, all eleven efferent vagus fibres which responded to changes in carotid sinus pressure also responded to distension of the urinary bladder by a decrease in activity. This response of a decrease in activity was obtained at all levels of carotid sinus pressure between 8.4 and 30 kPa, and was greater at high than at low carotid sinus pressure. In the same vagus fibres, a relation was shown between progressive decreases in activity and either increases in intravesical pressure up to 8.7 kPa or reductions in carotid sinus pressure between 9 and 30 kPa. The decreases in activity were greater at high than at low carotid sinus pressure. These findings have shown that the inhibition of vagus nerve activity caused by bladder distension was affected by the level of carotid sinus pressure.