During routine arteriographies in 10 patients with suspected vascular disease, the influence of arterially injected roentgen contrast media on the blood flow in the calf, the blood pressure in the common iliac artery and the heart rate were studied. The most important hemodynamic changes occurred within 20-30 seconds after the injection of the contrast medium (usually urografin 60 per cent) into the lumbar aorta. The systolic blood pressure then decreased, on the average, by 25 per cent and the diastolic by 13 per cent. The heart rate increased by about 20 per cent. The greatest blood flow increase (by 100-155 per cent) occurred between 30 and 70 seconds after the injection of the contrast medium. The vasodilative effect of the contrast medium was compared with the effect of physiologic saline and bradykinin.