Cerebral blood flow (CBF) was measured in 13 subjects (4 men and 9 women, mean age +/- SD = 63 +/- 7) with moderate, uncomplicated and untreated hypertension and 11 normotensive subjects (6 men and 5 women, mean age +/- SD = 66 +/- 5). A second CBF measurement was performed in hypertensive subjects after a 60 days randomized double blind treatment with either captopril, 75 mg a day (n = 8) or placebo (n = 5). CBF was quantified using the 133Xe inhalation technic and 16 stationary detectors by hemisphere. Comparison of CBF values between hypertensive subjects before treatment and normotensive subjects demonstrated a decrease of CBF in the hypertensive group (49 +/- 9 vs 72 +/- 14 ml/100 g/min; p < 0.001). After the trial the results in the captopril group showed a significant fall in systolic (p < 0.001) and diastolic (p < 0.05) blood pressure and a significant increase in CBF (60 +/- 14 vs 49 +/- 11 ml/100 g/min; p < 0.05). In the placebo group there was no change in blood pressure and CBF (Table). [Table; see text] Our results demonstrate a decrease in CBF of uncomplicated and untreated elderly hypertensive subjects. This decrease is reversible under chronic treatment with captopril.