Mutations in the mev-1 and gas-1 genes of the nematode Caenorhabditis elegans render animals hypersensitive to oxygen and paraquat, and lead to premature aging. We show that both mutants overproduce superoxide anion in isolated sub-mitochondrial particles, which probably explains their hypersensitivity to oxidative stress. The daf-16 gene encodes a fork-head transcription factor that is negatively regulated by an insulin-signaling pathway. In wild-type animals, the DAF-16 protein normally resides in the cytoplasm and only becomes translocated to nuclei upon activating stimuli such as oxidative stress. Conversely, DAF-16 resides constitutively in the nuclei of mev-1 and gas-1 mutants even under normal growth conditions. Supplementation of the antioxidant coenzyme Q(10) reversed this nuclear translocation of DAF-16. Since both gas-1 and mev-1 encode subunits of electron transport chain complexes, these data illustrate how mitochondrial perturbations can impact signal transduction pathways.