Following injury induced by oxidant stress (exposure to xanthine-xanthine oxidase during 120 min), cultured human umbilical vein endothelial cells were severely modified. These lesions were evaluated by electron microscopy and the types of injury were shown to be progressive cell blebbing as well as altered mitochondrial features. Enlargement of the endoplasmic reticulum and swelling of the Golgi apparatus were also observed. With the intention of learning more about the role of oxygen-derivative-induced alterations of the endocytotic apparatus (plasma membrane, endosomes, lysosomes), the receptor-mediated endocytosis of colloidal gold-conjugated LDL was evaluated. It was demonstrated that this endocytosis is drastically decreased following this type of injury, corroborating our previous report of important reduction in 125I-LDL endocytosis under the same conditions. Tubular electron-lucent structures, often observed in the vicinity of blebs, could possibly be involved in the impairment of LDL receptor accessibility.