The neurotoxic effects of oxygen radicals on spinal cord neuron cultures derived from fetal mouse have been studied. Oxygen radicals, superoxide radical and hydrogen peroxide, were generated by adding xanthine oxidase and hypoxanthine in the culture medium. Exposure of neurons to this oxygen radicalgenerating system resulted in a significant cell death and decrease of choline acetyltransferase (ChAT) activity in a time-dependent manner in spinal cord neuron cultures. The decrease in cell viability and ChAT enzyme activity induced by the oxygen radicals was blocked by scavengers such as superoxide dismutase (SOD), catalase, and tetrakis (2-pyridylmethyl) ethylenediamine (TPEN), a metal chelator. Antagonists of the N-methyl-D-aspartate (NMDA) receptor, including MK801 (a noncompetitive NMDA antagonist), D-2-amino-5-phosphonovaleric acid (APV) (a competitive NMDA antagonist), and 7-chlorokynurenic acid (an antagonist at the glycine site associated with the NMDA receptor), similarly blocked oxygen radical-induced decrease in cell viability and ChAT activity in spinal cord neuron cultures. These results indicate that both oxygen radicals and excitotoxic amino acids were involved in the oxidant-initiated neurotoxicity of spinal cord neurons.