Effects of various pressor amines on coronary circulation in anesthetized dogs were studied by the use of electromagnetic flow meter and coronary artreiography, 1) Intravenous administration of adrenaline, noradrenaline or isoproterenol resulted in increase of coronary blood flow. By coronary arteriography, these substances were noted to have dilating effect on coronary arteries of visible diameter.2) The increase of coronary blood flow was observed generally parallel to the rise of systemic blood pressure. However, in some instances, the increase of coronary blood flow continued even during the phase of the decreased blood pressure.3) The administration of isoproterenol caused the increased coronary blood flow and, at the same time, the decreased systemic blood pressure.4) The increase in coronary blood flow by these substances was inhibited by previous or concomitant administration of propranolol.5) Intracoronary administration of small dosis of adrenaline, noradrenaline or isoproterenol resulted in the increase of the maximum flow of diastolic phase and decrease of the minimum flow of systolic phase. These changes in the coronary blood flow were more prominent than the changes by intravenous administration of these substances in the same order of doses which should be expected.6) These results suggest that adrenaline, noradrenaline and isoproterenol may have the direct dilating effect on coronary artery.