The viability of bovine aortic endothelial cells (BAECs) treated with 0.1 mM H2O2 was decreased by 39.8%, and 100 mg/l EGb761 increased the viability by 20.6%. Exposure BAECs to H2O2 for 6 min resulted in a significant elevation in the intracellular free Ca2+. Pretreatment of BAECs with 10 mg/l and 100 mg/l EGb761 for 10 min showed a decrease in the intracellular free Ca2+, 4.5% and 20.6%, respectively. The apoptotic rate of BAECs measured by propidium iodide (PI) staining was (38.1 +/- 2%) after 18 h of treatment with H2O2. Pretreatment of BAECs with 100 mg/l EGb761 for 1 h reduced the apoptotic rate to 27 +/- 1%. In addition, there were about 5-7% of cells stained positive measured by TUNEL assay. When BAECs were exposed to 0.1 mM H2O2 for 18 h, the number of TUNEL-positive cells increased to 37-44%. When 10 mg/l EGb761 and 100 mg/l EGb761 were used, the TUNEL-positive cells decreased to 26.5 +/- 3.1% and 17.5 +/- 1.7%, respectively. Furthermore, EGb761 also inhibited caspase-3 activity induced by H2O2. It is concluded that EGb761 has protective effect on bovine vascular endothelial cells against damage induced by H2O2. Further studies are needed to clarify the mechanisms of action of EGb761.