Intravascular ultrasound is a new imaging modality which enables cross-sectional images of blood vessels. These preliminary results of intravascular ultrasound used before and after percutaneous transluminal angioplasty (PTA) in 19 patients, confirm earlier reports of the ability to distinguish between the three different layers of the vessel wall. Atherosclerotic plaques may also be assessed as well as a quantification of the stenosis. After PTA changes in the plaques such as intimal fractures, flaps and dissections could be recognized, and the effect of the intervention could be quantified by measuring the reduction of stenosis and increment of the luminal area. The increased luminal area following PTA was partly due to stretching of the artery and partly due to compression of the atheroma. We found a correlation between the amount of calcium in the plaque and the size of the dissection after PTA. Comparing IVUS with angiography revealed an acceptable agreement in quantifying stenoses before the intervention but not after. We conclude that IVUS is a feasible method to evaluate stenosis in blood vessels before and after PTA. By supplying additional information to angiography, it may improve the selection and outcome after PTA.