Oxidized low-density lipoprotein (ox-LDL) has been shown to alter the migratory and proliferative activities of the vascular endothelial cells (EC) in response to serum and growth factors. The mechanism underlying the antiproliferative effect of ox-LDL on vascular EC has not been fully elucidated. In this report, we show that exposure of vascular EC to ox-LDL results in a marked reduction of the membrane-associated Ras protein. Further study shows that in ox-LDL-treated EC, reduction of the membrane-associated Ras protein is correlated with a reduced amount of active Ras (Ras-guanosine triphosphate), indicating that the Ras signaling pathway is attenuated. The attenuation of the Ras signaling pathway in ox-LDL-treated EC may thus be responsible for the retarded response to the mitogenic stimulation of serum and growth factors.