The ultrasonic appearance of in vitro normal and atherosclerotic arterial wall was investigated with an intravascular ultrasound (IVUS) probe. Fresh cadaver specimens were used: two carotid, two aorta, four iliac and eight superficial femoral arteries. The wall of muscular arteries has a three-layered sonographic appearance. The central hypoechoic layer corresponds to the media, which is primarily composed of smooth muscle. Elastic arteries whose media have a high elastin content appear uniformly echogenic. Calcified plaque is strongly echogenic with acoustic shadowing, fibrous plaque is moderately echogenic, and where there is no cellular matrix the plaque is poorly echogenic. IVUS can provide information about internal plaque architecture. Three-dimensional reconstructions can be generated using a transputer-based workstation coupled to the transducer, providing detailed views of surface contour.