This paper aimed to investigate the therapeutic effect of an extract of Ginkgo biloba leaves (EGb 761) on hypertension and its possible mechanisms in the view of cerebral microcirculation. Twenty normotensive rats and 24 SHR rats were used. Surgical preparation was made to produce a cranial window for observation of the capillary network on the cerebral cortex. The intravital videomicroscopy equipped with digital image processing system and laser Doppler flowmeter were used for this study. The arterial blood pressure, red cell velocity (V), microvacular diameter (D), number of open capillaries (OCN), circulating endothelial cells (CEC) in blood, relative blood flow (Flow) and frequency (Fc), amplitude (AMP) of vasomotion were measured. The obtained data were compared between EGb-treated rats that received per os 100 mg/kg/d for 9 days and placebo control rats. Untreated SHR rats showed very severe dysfunction in the microcirculation with high blood pressure (213 +/- 16.7 mmHg). The blood pressure decreased significantly to 153 +/- 20 mmHg in EGb-treated SHRs group, compared with those of untreated rats (p < 0.01). Both normotensive and hypertensive rats increased the blood flow velocity and LDF flow after EGb-treatment. The vasomotion property, the CEC and OCN changed greatly in EGb-treated SHR rats, but no significant difference was observed in normotensive rats. It was suggested that EGb 761 had therapeutic effect on SHR rats by increasing blood perfusion, regulating vasomotion function, opening efficiently capillaries and releasing the peripheral resistance. The injured vascular endothelium of SHR rats was also partly reversed by EGb-treatment. It was concluded that EGb 761 could be used to regulate hypertension and to protect the cerebral microcirculatory function.