Oxidative modifications of blood serum in humans with and without coronary artery disease were investigated. Four parameters were analyzed: the intensity of serum fluorescence, which is indicative of the content of lipofuscine-like lipid peroxidation products; the content of thiobarbituric acid-reactive substances; the lag-phase of serum oxidation by azo-compounds; and the content of lipophilic natural antioxidants--alpha-tocopherol, beta-carotene and ubiquinol-9(10). It was found that coronary artery disease resulted in a significant increase of serum fluorescence and the content of TBARS. The atherogenic disorders in humans with coronary artery disease drastically decreased the lag-phase of serum oxidation in the presence of 2,2'-azo-bis-(2-amidinopropane) dihydrochloride. The oxidative modifications of serum were in close correlation with the balance of natural lipophilic antioxidants in blood serum, i.e. alpha-tocopherol, ubiquinols and beta-carotene. The contents of all antioxidants tested in serum were significantly decreased in patients with coronary artery disease.