We examined the effect of menadione on the morphology and viability of cultured astrocytes. Exposure of astrocytes to menadione induced a progressive cell death. The toxic effect of menadione was concentration- and time-dependent. Menadione toxicity was blocked by antioxidants, superoxide dismutase, catalase and iron chelators, indicating that superoxide anions (O2-), hydrogen peroxide (H2O2) and hydroxyl radicals (.OH) are all involved in menadione toxicity. Menadione cytotoxicity should be useful as a model for studying the mechanisms underlying oxidative injury in the brain and for the screening of drugs that may attenuate cell damage caused by oxidative stress.