This study evaluated the dimensional and morphologic precision of arterial images obtained using intraluminal rotating A-scan ultrasound catheters [5.0F (30 mHz) and 8.0F (20 mHz)]. Dimensions of in vitro ultrasound images from human arteries (eight normal and nine arteriosclerotic) were compared with those from histologic sections of the vessels. In addition, in vivo ultrasound studies (23 normal and 22 arteriosclerotic) of canine femoral arteries were compared with luminal dimensions obtained from angiograms of the vessels. The correlation of in vitro ultrasound images to luminal diameters (n = 22, r = 0.96), adventitial diameters (n = 19, r = 0.83), and wall thickness (n = 19, r = 0.68) in normal human vessels was significant (p less than 0.05). In vitro measurements of images and histologic specimens from human atherosclerotic arteries also correlated significantly (p less than 0.05) with luminal diameters (n = 27, r = 0.91), adventitial diameters (n = 24, r = 0.60), and wall thickness (n = 24, r = 0.62). Morphologically, in vitro images of the wall of normal human arteries had a concentric laminated appearance and atherosclerotic vessels had patchy echodense and echolucent areas. In vivo studies showed significant correlation of diameters for both normal (n = 16, r = 0.91, p less than 0.05) and arteriosclerotic (n = 16, r = 0.57, p less than 0.05) canine arteries compared with luminal dimensions measured from uniplanar angiograms. We conclude that rotating A-scan intraluminal ultrasound accurately defines both normal and atherosclerotic arterial wall morphology and dimensions. This technology may be valuable for intravascular guidance of angioplasty devices by identifying the location and consistency of lesions.