Arterial stiffness is a predictor of cardiovascular disease and all-cause mortality. Arteries stiffen with age and a result of lifestyle influences and some disease states which places a greater load upon the heart. The stiffness of arteries is determined by the structure of the artery wall and the tension applied by smooth muscle within the artery wall. Smooth muscle tone is controlled by many factors, one of which is sympathetic nerve inputs. This study identifies the extent to which sympathetic activity affects large artery haemodynamics in both the normotensive and hypertensive condition. Following removal of sympathetic nerve activity via injection of hexamethonium (20 mg/kg) normotensive rats (WKY, n=7) showed a significant increase in aortic diameter, compliance and distensibility at operating blood pressure (100 mm Hg). However, within hypertensive rats (SHR, n=9), the increase in aortic diameter following injection of hexamethonium was not accompanied by a change in any measured stiffness parameters at operating blood pressure (150 mm Hg). These results reflect both the contribution of sympathetic nerve activity to arterial haemodynamics as well as the differential influence of sympathetic input on arteries that have developed under different pressure states. These results should help contribute to the understanding of the relationship between hypertension, arterial stiffness and sympathetic nerve activity in man.