Dynamics of alterations in activities of catalase, superoxide dismutase (SOD), glutathione-peroxidase (GPx) and-reductase (GR) as well as shifts in content of malonic dialdehyde and in oxidative index values were studied in erythrocytes of 108 persons after the red blood cells contact with molecular oxygen within 70 min; a decrease in values of oxidative index and activation of the enzymatic activity studied were found All the alterations observed were distinctly higher in erythrocyte membranes and depended on the membranes structure and initial activity of the membrane-bound antioxidative enzymes. Treatment of erythrocyte membranes with solutions of high ionic strength showed that catalase and SOD were less rigidly bound to membrane as compared with GPx and GR. Distribution of SOD, GPx and GR activities was similar to normal values in the membranes, while the catalase activity distribution did not follow the Gauss equation. Thus, erythrocyte membranes were divided into two types, depending on the rate of catalase activity (high or low). The first type of membranes with high catalase activity were found to be resistant to peroxidation, exhibited high activity of SOD and low activity of GPx, content of cholesterol was decreased in these membranes.