Intravascular ultrasound imaging was performed in 15 patients (three women and 12 men; mean age 55 [48-70] years) after percutaneous balloon angioplasty of the right coronary artery (7 patients), the anterior interventricular branch (6) or the circumflex branch of the left coronary artery (2). The catheter, external diameter 4.8 F, was advanced over a 0.014--in coronary wire to the area of the previously balloon-dilated stenosis. Vessel diameter measured by ultrasound correlated closely with that by angiography (r = 0.93; P less than 0.001). Ultrasound imaging distinguished between concentric and eccentric intimal thickening and made it possible to assess the consistency and degree of calcification of the wall changes. The success of angioplasty was evaluated in 10 patients. In eight, local dissection was revealed, but only three of them had been diagnosed angiographically. In one patient a vessel spasm was recorded during ultrasound imaging; it regressed after the intracoronary injection of 0.2 mg nitroglycerin. There were no other complications. The method made it possible to assess in vivo the extent and consistency of atherosclerotic plaques, and it adds to the angiographic monitoring of treatment results and of complications after angioplasty.