One of the present writers (NORDENSTROM 1954) described the appearances of small vascular vessels, such as the intercostal and bronchial arteries following the injection of contrast medium above an occlusion of the thoracic aorta in the dog. The very small bronchopulmonary arterial vessels that are considered of importance for, inter alia, the blood supply to malignant tumours might possibly also be examined by this method in human subjects.Occlusion of the aorta in man has earlier been performed without complications in connection with operations (CRAFOORD 1945) although damage to the spinal cord has also been recorded. Such damage has occurred in operations upon coarctation of the aorta, despite the fact that the collaterals are thought to afford possibilities for a more protracted occlusion than when the aorta is normal (BING et call. 1948). Occlusion of the aorta distal to the origin of the left subclavian artery has also been possible without complications for up to 45 minutes in operations upon aortic aneurysms (BAHNSON 1953, LAM et colI.