On the basis of a large number of reports concerning the detection of lipid peroxidation products as biomarkers in human diseases, there is no doubt that their steady-state levels increase under pathophysiological states associated with oxidative stress. The key question is whether they play any causative roles. This may be a matter of primary concern, which represents an important direction to pursue in the future of toxicology. My latest approach from autoimmune response induced by lipid peroxidation products will be illustrated.