Our data indicate that changes in blood plasma FA composition in patients with MODS are mainly caused by activation of lipolysis in fat depots and are accompanied by an increase of monounsaturated fatty acids, a decrease in saturated stearic acid and polyunsaturated fatty acids in the ratio. In conditions of increased level of monounsaturated palmitoleic (C16:1) and oleic (C18:1) FA in blood plasma (2.53 ± 0.40% vs. 1.55 ± 0.29%, P < 0.001 and 25.18 ± 2.15% vs. 16.55 ± 1.17%, P < 0.001, respectively), only the level of palmitoleic (C16:1) acid is increased in erythrocytes (0.56 ± 0.12% vs. 0.16 ± 0.12%, P < 0.001). Despite the high content of oleic (C18:1) acid in blood plasma in case of MODS, in erythrocytes its relative level is not changed as compared with the control group. The disorder of lipid composition constancy in erythrocyte membranes is also manifested by change in the content of saturated palmitic (C16:0) and polyunsaturated linoleic (C18:2) fatty acids. In the test group of patients, as compared with the control group there was an elevated level (27.12 ± 0.78% vs. 25.80 ±0.77%, P < 0.05) of saturated palmitic (C16:0) acid combined with the reduced (11.46 ± 0.52% vs. 13.95 ± 1.09%, P < 0.001) level of linoleic (C18:2) acid.