Colorectal cancer is still a major medical, economical and public health problem. Pathogenesis of colorectal cancer remains unknown. It is thought both genetic and environmental factors contribute to the etiology and progression of the disease. Reactive oxygen species are known to play a dual role in biological systems they can be either harmful or beneficial. Oxygen-free radicals are important mediators of damage to cell structures, including lipids, proteins and nucleic acids. Radical-related damage to cell structures has been proposed to play a key role in the development of many diseases including cancer.Humans have evolved complex antioxidant strategies to protect cells from oxidation.Total antioxidant capacity (TAC) considers the cumulative action of all the antioxidants present in plasma or other body fluids.The aim of the study was to investigate antioxidant status in patients with colorectal cancer measuring plasma TAC as a tool.Material and methods. The study group comprised 102 patients in different clinical stages operated on for colorectal cancer. To evaluate plasma total antioxidant capacity we used "Total Antioxidant Status Kit" - RandoxResults. Statistical evaluation of results demonstrated significantly lower serum total antioxidant capacity in patients with colorectal cancer, as compared to the healthy control group. We observed increase mean plasma total antioxidant capacity correlating with decrease of clinical disease stage.Conclusions. Colorectal patient have impairment antioxidant barrier. The deterioration of its functioning corresponds with the stage of the disease.