To appraise the value of transcranial Doppler sonography (TCD) for assessment of hypertensive cerebrovascular damage, the relationship between ambulatory blood pressure (BP) and indices of cerebral circulation determined by TCD was investigated. Subjects were 55 inpatients with or without hypertension, including 13 patients with histories of cerebrovascular attacks. Mean flow velocity (MFV) in the middle cerebral artery was measured by TCD, then the cerebrovascular resistance index (CVRI; mean BP/MFV) and the Fourier PI₁ (pulsatility index of the first Fourier harmonic of the flow-velocity waveform) were determined as indices of cerebrovascular resistance. CO₂ reactivity of MFV was estimated as an index of cerebrovascular flow reserve. CVRI positively correlated with both daytime and nighttime BP as well as with age (p<0.01). Fourier PI₁ positively correlated with nighttime BP and age (p<0.01). CO₂ reactivity did not correlate with any of the ambulatory BP parameters, but negatively correlated with age (p<0.01). LV mass index significantly correlated with ambulatory BP parameters, CVRI, and Fourier PI₁, but did not correlate with CO₂ reactivity. Multiple regression analyses showed that nighttime systolic BP was a significant correlate for CVRI and Fourier PI₁, but not for CO₂ reactivity, and that history of cerebrovascular attack was significant for CVRI and CO₂ reactivity. We conclude that cerebrovascular resistance determined by TCD accords with the results of ambulatory BP and LVMI, and thus could be successfully used to detect the early stage of hypertensive cerebrovascular change. Cerebrovascular flow reserve would be relatively preserved in hypertensive patients without cerebrovascular diseases. (Hypertens Res 2001; 24: 345-351)