Changes of vascular relaxation after balloon denudation of the rabbit aorta were investigated. Endothelium-dependent relaxation of ballooninjured vessels to acetylcholine was reduced significantly, 27. 7±9. 9% and 51. 1± 11. 4% of control at 2and 4 weeks after denudation, respectively. However,sodium nitroiprusside-induced relaxation and noradrenaline-induced contractile remained unchanged in the denuded vessel rings. After balloon denudation,vascular smooth muscle cell proliferation increased,and intima thickened. These findings indicated that function of vascular endothelinm-dependent relaxation was injured, and endothelum-derived relaxing factor production may diminished after balloon denudation.Vascular smooth muscle cell proliferation was related to these changes.