Pulsatile changes in the volume of an arm segment were recorded with an air-filled plethysmograph and related to intra-arterial blood pressure. Alterations in transmural arterial pressure were obtained by changing the pressure in a large chamber surrounding the entire arm. Arterial compliance values were calculated in late diastole when pressure and volume changes were slow. Compliance varied with transmural arterial pressure in a hyperbolic manner, rising steeply at low pressure. Noradrenaline and hypertensin did not change the arterial compliance values, while dihydroergotamine reduced them. Nitroglycerine caused a pronounced increase in compliance values in doses that did not change cardiac output and arterial pressure.