Enzymes represent a very important component of the antioxidative system of the organism. The principal role in elimination of free radicals is played by superoxide dismutase which catalyzes conversion of superoxide to hydrogen peroxide. This compound is then metabolized in subsequent reactions in which catalase and peroxi- dases, especially glutathione peroxidase, participate. Finally, paraoxonase prevents the negative effect of free radicals by hydrolyzing oxidative products in low-density lipoproteins. The authors discuss the above mentioned enzymes in detail: they notice their function, structure, and location in the cell and describe the states which lead to their increased or decreased activity as well as the consequences of a hereditary defect of enzyme synthesis.

        Key words: free radicals, reactive oxygen species, antioxidants, superoxide dismutase, catalase, glutathione peroxidase, paraoxonase.