BACKGROUND: Free radical reactions are a part of normal human metabolism. When produced in excess, radicals can cause tissue injury. The present study was aimed to investigate neurotoxic effect of oxygen free radicals and neuroprotective effect of antioxidant(glutathione). METHODS: Neurotixic effect of oxygen radicals was evaluated by MTT[3-(4,5-dimethylthiazol-2,5- diphenyltetrazolium bromide] assay and neurofilament enzyme-immunoassay after culturing of spinal motor neuron cell line of mouse(NSC-34). Then these cells were exposed to various concentrations of xanthine oxidase(XO) and hypoxanthine(HX). In addition, neuroprotective effect of antioxidant against oxidant-induced neurototoxicity on these cultures was examined. RESULTS: Exposure of neurons to 25mU/ml XO and 0.2mM HX for 3 hours resulted in a significant cell death and also glutathione(GSH) blocked the neurotoxicity induced by oxygen radicals in cultured mouse spinal motor neurons. CONCLUSION: From the above results, it is suggested that oxygen radicals are toxic in NSC-34. Selective antioxidants such as GSH are effective in blocking oxidant-induced neurotoxicity on these cultures.