In this study, lipid peroxide and glutathione (GSH) levels, GSH peroxidase, GSH S-transferase, superoxide dismutase, gamma-glutamylcysteine synthetase and gamma-glutamyl transpeptidase activities were investigated in tumorous and nontumorous colorectal tissues obtained from ten patients diagnosed with colon and rectum cancer. Histopathological evaluations, including type, stage, necrosis and lymphocyte infiltration, were also performed for each patient. According to the results, lipid peroxide and GSH levels and the activities of GSH peroxidase, superoxide dismutase, gamma-glutamylcysteine synthetase were found to be increased, while GSH S-transferase and gamma-glutamyl transpeptidase activities remained unchanged in tumors compared to adjacent normal tissues of subjects with colorectal cancer. However, the considerable interindividual variations were found in these parameters. A definite interrelation between histopathological results with lipid peroxidation and antioxidant system was not observed.