The present investigation was undertaken to examine the blood levels of lipid peroxides and the antioxidants superoxide dismutase, catalase, reduced glutathione, glutathione peroxidase, and glutathione-S-transferase in oral precancer, preoperative, postoperative, and recurrent oral cancer patients with age- and sex-matched normal healthy subjects as controls. In patients with oral precancer and oral cancer, enhanced lipid peroxidation was accompanied by antioxidant depletion. These changes were more pronounced in patients with recurrent oral tumors. Twelve weeks after surgery, decreased lipid peroxidation was accompanied by increased antioxidant levels. The results of this study indicate that imbalance in the redox status of oral cancer patients may be due to enhanced lipid peroxidation and compromised antioxidant defenses.