In this study, we show that reactive oxygen species production induced by tumour necrosis factor alpha (TNF-alpha) in L929 cells was associated with a decrease in the steady-state mRNA levels of the mitochondrial transcript ATPase 6-8. Simultaneously, the transcript levels of two nuclear-encoded glycolytic enzymes, glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and phosphofructokinase, were increased. These changes were associated with decreased protein levels of the ATPase subunit a (encoded by the mitochondrial ATPase 6 gene) and cytochrome c oxidase subunit II, and increased protein levels of phosphofructokinase. Since TNF-alpha had no effect on the amount of mitochondrial DNA, the results suggested that TNF-alpha acted at the transcriptional and/or post-transcriptional level. Reactive oxygen species scavengers, such as butylated hydroxianisole and butylated hydroxytoluene, blocked the production of free radicals, prevented the down-regulation of ATPase 6-8 transcripts, preserved the protein levels of ATPase subunit a and cytochrome c oxidase subunit II, and attenuated the cytotoxic response to TNF-alpha, indicating a direct link between these two phenomena.