The effects of four edible oils on lipid peroxidation have been investigated in rabbit heart mitochondrial membranes. The experimental oils (olive oil from the variety "picual", washed olive oil from the variety "picual", olive oil from the variety "arbequina" and high-oleic sunflower oil) had a similar fatty-acid composition, but differed in their unsaponified fraction (polyphenols, tocopherols, and others). The lowest hydroperoxide levels were found with picual and washed picual. No differences in mitochondrial membrane thiobarbituric acid reactive substance (TBARS), alpha-tocopherol concentrations and cytosolic antioxidant enzymes (superoxide dismutase, glutathione peroxidase, glutathione reductase and catalase) were found, whereas the CoQ10 content correlated inversely with hydroperoxide levels in all groups. These results suggest that mitochondrial membranes with high levels of monounsaturated fatty acids generate low levels of lipid peroxidation. Moreover, the saponified fraction of the experimental diets proved more important in preventing lipid peroxidation than the unsaponified fraction. Lastly, coenzyme Q may help to prevent peroxidative stress damage in rabbit heart mitochondria.