Noninvasive flow dynamics in 69 [human] carotid arteries following endarterectomy were studied. Using 3 parameters which measure changes in velocity or disturbed flow, 49% of the arteries demonstrated flow abnormalities consistent with a 50% or greater reduction in diameter in at least 2 of the 3 measured parameters. Of the 31 arteries which underwent > 1 postoperative study, progression of the flow abnormality was suggested by changes in the velocity ratio in 20 arteries, maximum velocity in 15 arteries and the fractional broadening term in 25 arteries.