Accumulating data suggest a central role for mitochondria and oxidative stress in neurodegenerative apoptosis. We previously demonstrated that amyloid-beta peptide 25-35 (Abeta 25-35) toxicity in cultured cells is mediated by its effects on functioning mitochondria. In this study, we further explored the hypothesis that Abeta 25-35 might induce apoptotic cell death by altering mitochondrial physiology. Mitochondria in Ntera2 (NT2 rho+) human teratocarcinoma cells exposed to either staurosporine (STS) or Abeta 25-35 were found to release cytochrome c, with subsequent activation of caspases 9 and 3. However, NT2 cells depleted of mitochondrial DNA (rho0 cells), which maintain a normal mitochondrial membrane potential (Deltapsi(m)) despite the absence of a functional electron transport chain (ETC), demonstrated cytochrome c release and caspase activation only with STS. We further observed increased reactive oxygen species (ROS) production and decreased reduced glutathione (GSH) levels in rho+ and rho0 cells treated with STS, but only in rho+ cells treated with Abeta 25-35. We conclude that under in vitro conditions, Abeta can induce oxidative stress and apoptosis only when a functional mitochondrial ETC is present.