Objective. To assess whether a correlation between perfusion changes to visual stimulus on the bilateral occipital areas and blood flow velocity changes to visual stimulus in both posterior cerebral arteries is present. Methods. Nine right-handed healthy subjects (4 women and 5 men, mean +/- SD age, 58.0 +/- 5.6 years) were included in the study. Visual stimulation was per-formed in room light with the subject's eyes open and looking around versus eyes closed as the stimulus-off condition. The blood flow velocities were recorded using transcranial Doppler sonography, and the regional cerebral blood flow measurements were recorded with the use of technetium Tc 99m exametazime and a single photon emission computed tomographic gamma camera system. individual reactivity was defined as a relative increase of blood flow velocity and perfusion, which were calculated as percentage changes of baseline values. Results. Visual stimuli produced a marked increase of blood flow velocity in both posterior cerebral arteries (35.2 +/- 2.3 cm/s; P <.001) without a significant side-to-side difference in all subjects as well as a marked increase of perfusion on both occipital areas (24.9 +/- 4.8 cm/s; P <.01). Moreover, there was a positive correlation between blood flow velocity changes and perfusion changes on both sides (r = 0,833; P <.01). Conclusions. The use of bilateral simultaneous Doppler recordings by means of a flow velocity averaging algorithm to a specific stimulus allows quantitative assessment of blood flow responses, and simple visual stimuli can be applied for different disorders to assess the vasomotor regulation that may result in measurable abnormal cerebral flow regulation even when clinically stabilized.