Although oxidative stress and mitochondrial dysfunction have been linked to neurodegenerative diseases such as Alzheimer's disease (AD), it is not fully understood how mitochondrial oxidative stress may induce neuronal death. We used mitochondrial transgenic neuronal cell cybrid models of sporadic AD (SAD) to investigate the effects of endogenously generated reactive oxygen species (ROS) on viability and cell death mechanisms. Compared to control (CTL) cybrids, SAD cybrids have increased accumulation of oxidative stress markers and increased apoptosis that is blocked by N-acetylcysteine (NAC) and zVAD.fmk. SAD cybrids also have increased basal activation of the MAPKs, Akt, and NF-kappa B. NF-kappa B activation and cybrid viability are enhanced by NAC. Inhibiting the activity of the PI3K pathway or NF-kappa B aggravates neuronal death. Exposure of CTL cybrids to H2O2 decreased viability and activated in a NAC-sensitive manner, the same intracellular signaling pathways active under basal conditions in SAD cybrids.