Eight patients with subclavian artery stenosis or occlusion and transient cerebral ischemia or brachial claudication were treated with a carotid-subclavian bypass. Intraoperative measurement of graft flow and carotid and subclavian pressure indicated restoration of subclavian pressure in all but one patient with a small vein graft. Graft flow increased from 149 ± 28 to 408 ± 55 ml/min with injection of 15 mg of papaverine hydrochloride into the graft. Carotid pressure did not fall when the graft was opened and fell an average of 2 mm Hg after papaverine. These hemodynamic observations support the use of carotid-subclavian bypass and indicate that the common carotid artery is adequate to supply the distal carotid and subclavian arteries unless there is proximal stenosis of the common carotid.