Lipid peroxidation is an important mechanism in free radical mediated cell injury. It can damage cell membranes directly and the reactive carbonyl products may spread the damage far from the original site of radical production. It has long been considered to be involved in various toxic tissue injuries and in certain disease processes, including cancer. Paradoxically, cancer cells are very resistant to lipid peroxidation. Recently, it has been suggested that lipid peroxidation may exert more subtle effects than was previously thought possible, by influencing gene expression.