Eighteen patients with chronic totally occluded coronary arteries underwent percutaneous coronary angioplasty. Eleven of these patients had a proximal occlusion of the left anterior descending artery and seven had occlusion of either the proximal or middle right coronary artery. All patients had severe angina pectoris with clearly positive results of stress treadmill testing. Preservation of a viable myocardium despite an occluded artery was, in each instance, the result of excellent collateral flow arising from the contralateral coronary artery. The guide wire and the dilatation balloon were properly positioned by opacifying the distal segment of the occluded artery by injection of contrast into the contralateral artery in 15 of 18 patients. Almost simultaneous injection, first into the contralateral vessel and then into the occluded artery, allowed evaluation of the true length of the occlusion. Contralateral opacification disappeared immediately after adequate recanalization and reappeared during inflation of the balloon. These examples show that in patients with chronic coronary occlusion, opacification of the distal segment by injection of contrast into the contralateral vessel seems to be helpful and without risk to the patient.