Effects of Ginkgo biloba extract (EGb 761) on the anti-pulmonary hypertensive action of enalapril were evaluated in rats. Pulmonary hypertension was induced by monocrotaline treatment (60mg/kg, i.p.) in normotensive rats. In the systolic pulmonary artery pressure, the control group was 33$pm$2 mmHg, comparing to the normal group of 19$pm$1 mmHg. That of enalapril group(20mg/kg/day, p.o.) was 26$pm$2 mmHg. In the isolated lung preparation, acetylcholine, which was endothelium dependent vasodilator, induced the decrease of pulmonary artery perfusion pressure(-2.0$pm$0.7 mmHg) in normal group, but the increase of that of 3.4$pm$0.6 and 3.0$pm$0.9 mmHg in control and enalapril group, respectively. And that of the combined group was -0.5$pm$0.2 mmHg. In the isolated pulmonary artery, acetylcholine(10-5M) induced the relaxation of 65$pm$6% in normal group, but 15 and 8% in control and enalapril group, respectively. And that of the combined group was resulted 55$pm$2%. These results suggested that co-administration of Ginkgo biloba extract(EGb 761) potentiated the anti-pulmonary hypertensive effects of enalapril through the increase of pulmonary vasodilation due to the protection of endothelial cell by antioxidant action of Ginkgo biloba extract (EGb 761).