Cerebral SPECT with 99mTc-HM-PAO allows a semiquantitative evaluation of regional cerebral blood flow (rCBF). Using this method we studied 25 patients affected by slight-to-moderate degree hypertension, in effective pharmacological treatment, and a control group of normotensives. On the cross-sections symmetrical ROIs were traced at the level of the cerebral lobes and the cerebellum. From the counts obtained on the ROIs the rCBF values were calculated in percentage units with Lassen's algorithm. We found no significant differences between the rCBF values of the two groups. In 5 hypertensive patients, however, focal areas of hypoperfusion were evidenced. These patients did not differ from the other hypertensives by pressure levels or other risk factors. Neurological, tomographic and flowmeter examinations of the supraaortic arteries proved to be normal. It is possible that SPECT with 99mTc-HM-PAO identifies a subgroup of hypertensives at risk of future cerebrovascular pathology despite the setting up of an effective antihypertensive therapy.