SUMMARY Power Frequency Spectral Analysis (PFSA) which evaluates the power of the frequency components at a selected interval, was applied in this preliminary study using a 5MHz Doppler continuous wave flow velocity meter and a modified Edwards Spectra view 500 analyzer.PFSA was used to study the common, internal and external carotid arteries of ten young adult control subjects and 31 patients with angiographically documented carotid bifurcation lesions. Two useful indices are described: (1) the frequency band width at 50% of maximum power (f M% ) and (2) the highest frequency recorded (J^J-An fj,,^ wider than 1900 Hz (corresponding to spectrum broadening) identified stenoses as low as a 15% diameter reduction. An t nux higher than 6500 Hz practically always indicated a 50% or greater diameter reduction.Eighty two percent of stenoses with 11-25% diameter reduction were detected, as were 95% of stenoses from 36-50%. All stenoses from 51-99% were identified.