The coronary arteries have been visualized in unanesthetized patients by injecting a radiopaque medium through a catheter into the ascending aorta. After premedication with meperidine and atropine, the catheter is introduced by way of the brachial artery and inserted until its tip lies about 2.5 cm. above the aortic valve. Special techniques have been developed in order to predetermine the phase and duration of the injection, since 40 to 55 cc. of the radiopaque medium must be injected within 0.8 to 0.6 seconds and the subsequent film exposures must be properly timed. The most convincing sign of coronary artery disease is the roentgenographic finding of occlusion of a major vessel. Of the four illustrative case histories here given, two concern patients who had been considered for cardiac surgery because of signs and symptoms of angina pectoris; the arteriographic demonstration of normal coronary systems in both cases was decisive in planning subsequent treatment. Recently injections have been made during the first half of the cardiac cycle starting at systole. This has reduced the volume of contrast material needed by half without affecting the clarity of the arteriogram. In over fifty studies there have been no complications. Copyright, 1958, By American Medical Association.