The possibilities at ordinary thoracic aortography, with free flow in the aorta, of obtaining satisfactory filling of small vessels arising from the aorta are restricted. Injections above an occlusion of the aorta were made in experiments in animals and reported by the present writer in 1954 and in man 1955 in order to improve the examination conditions. The risk of damage to the spinal cord, apparent in the experiments in animals with the contrast media then available, contra-indicated any further investigations of this type in man. A systematic series of investigations of the toxicity of new contrast media made it possible to continue the examinations in human subjects later, with injection above the occlusion. Parallel with these investigations, the catheterization technique was being further developed. In the first examinations with balloon occlusion of the aorta, a double-lumen catheter provided with a balloon was introduced into the descending aorta after exposure of the radial artery. The balloon was filled through one lumen and the contrast medium injection was made through the other. Certain difficulties were however encountered in introducing the relatively large catheter with the balloon into the radial artery.