The extent of lipid peroxidation and DNA damage induced by quercetin were studied under aerobic conditions in isolated rat-liver nuclei. The effects of iron and copper ions on these two toxic oxidative processes were also investigated. Quercetin induced significant (P less than 0.05) concentration-dependent nuclear lipid peroxidation concurrent with DNA degradation; these effects were enhanced by iron and copper ions. The results suggest that the reactive oxygen species generated by quercetin autoxidation, catalyzed by iron and copper ions, are responsible for the concurrent lipid peroxidation and DNA damage in isolated rat-liver nuclei.