A 20 MHz pulsed Doppler velocimeter and fast Fourier transform spectrum analyzer were used at operation to assess the velocity patterns just prior to and immediately following carotid endarterectomy (TEA). In all 45 sides studied, the status of the endarterectomized segment was verified by operative arteriography. Corresponding Pre-TEA and Post-TEA internal carotid artery spectra were compared to each other and classified according to criteria developed using the ultrasonic Duplex scanner. Of 39 arteries with significant Pre-TEA flow disturbances, improvement in Post-TEA spectral characteristics was observed in 35, and 4 were not changed. Six arteries had only minimal flow disturbances both before and after endarterectomy. In one case the initial Post-TEA spectrum showed a worsening of the flow disturbance which was found on operative arteriography to be due to a stenosis secondary to a technical error. After vein patch angioplasty, the spectrum and repeat arteriogram were both improved. No other significant technical problems were encountered. Although the velocity patterns were improved by endarterectomy in most cases, some residual flow disturbance often remained. Technical factors were not a major cause of the Post-TEA flow disturbances. Lack of improvement or deterioration in the spectra after closure of the arteriotomy may be useful in selecting patients for operative arteriography. Intraoperative spectra also provide important baseline data for long term followup studies.