1. The effects of mechanical activation of aortic sympathetic sensory fibres have been studied in conscious dogs.
2. A cannula covered by an inflatable rubber balloon, previously implanted in the descending thoracic aorta, was used to stretch the aortic walls without obstructing blood flow.
3. Aortic stretch significantly increased mean arterial blood pressure and heart rate from control values in the absence of pseudo-affective reactions.
4. This response indicates that positive feedback sympathetic reflexes are operative in the conscious, fully innervated animal.