The work was aimed at elucidating the role of the indices of the antioxidant system (AOS) of the blood and nitrogen oxide content in differential diagnosis of atherosclerosis obiiterans (AO) and thromboangiitis obiiterans (TO) of the lower extremities. Presented herein are the findings of examining a total of one hundred and thirteen 30-to-45-year-old patients (of these, 60 had TO and 53 had AO) with various level of occlusion (from the femoropoplietal segment to the aortoiliac zone) and the stage of chronic arterial insufficiency (CAI IIA-IV). The control group was composed of 30 apparently healthy age-matched male subjects. Besides the clinical, laboratory and special instrumental methods of study, we determined the parameters of the AOS of blood and the content of nitrogen oxide degradation products. It was determined that the directedness and pronouncedness of deviations in the parameters of the AOS and nitrogen oxide from the physiological norm depended on not only the aetiology of the disease involved, but on the degree of tissue hypoxia predetermined by the stage of CAI of the lower limbs. For differential diagnosis between AO and TO, the most informative should be considered the coefficient: SOD activity/catalase activity, index of peroxide-luminol-dependent chemiluminescence and the content of nitrogen oxide degradation products.