Apoptosis of vascular smooth muscle cell (VSMC) plays an important role in the genesis of atherosclerosis and restenosis. In order to investigate the role of reactive oxygen species in the induction of VSMC apoptosis, rat VSMCs were treated with glucose oxidase/glucose (GO/G) or diethylmaleate (DEM). The results showed that GO/G and DEM led to VSMC death. Administration of catalase, superoxide dismutase and deferoxamine revealed that H2O2 was the major reactive oxygen species causing cell death, and H2O2O exerted its effect by formation of hydroxyl radical (.OH). GO/G- and DEM-induced VSMC death occurred by apoptosis characterized by "DNA ladders", condensation of nuclei, positive to in situ nick-end labeling and increases in histone-associated DNA fragmentation. This study suggests that H2O2 and its derived form .OH might be related to apoptosis of VSMC in atherosclerosis and restenosis.