The mechanism by which β-amyloid protein (Aβ) causes degeneration in cultured neurons is not completely understood, but several lines of evidence suggest that Aβ-mediated neuronal death is associated with an enhanced production of reactive oxygen species (ROS) and oxidative damage. In the present study, we address whether supplementation of glucose-containing culture media with energy substrates, pyruvate plus malate (P/M), protects rat primary neurons from Aβ-induced degeneration and death. We found that P/M addition attenuated cell death evoked by β-amyloid peptides (Aβ25–35 and Aβ1–40) after 24 hr treatment and that this effect was blocked by α-ciano-3-hydroxycinnamate (CIN), suggesting that it requires mitochondrial pyruvate uptake. P/M supply to control and Aβ-treated neuronal cultures increases cellular reducing power, as indicated by the ability to reduce the dye 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT). The early increases in ROS levels, measured by dichlorofluorescein (DCF) fluorescence, and caspase-3 activity that follow exposure to Aβ were notably reduced in the presence of P/M. These results place activation of caspase-3 most likely downstream of oxidative damage to the mitochondria and indicate that mitochondrial NAD(P) redox status plays a central role in the neuroprotective effect of pyruvate. Inhibition of respiratory chain complexes and mitochondrial uncoupling did not block the early increase in ROS levels, suggesting that Aβ could initiate oxidative stress by activating a source of ROS that is not accesible to the antioxidant defenses fueled by mitochondrial substrates. © 2003 Wiley-Liss, Inc.