Spin probes were used to study alteration of red cell membranes in nephropathy of varying degree of gravity. Iminoxyl radicals of the lipid nature were applied as spin probes, in particular 2-(3-carboxypropyl)-4,4-dimethyl-2-tridecyl-3-oxazolidinyl (probe I). It was shown that in nephropathy, the orderliness parameter increases and the hydrophoby of probe I localized in a red cell suspension of nephropathy patients diminishes as compared with analogous parameters in healthy pregnant women. This attests to both immobilization of the fatty acid chains of phospholipids and to an increase in the polarity of the lipid bilayer in the area of probe localization. It was established that diminution of probe I hydrophoby is in a satisfactory agreement with the disease gravity and the degree of edema in patients. It was noted that alterations discovered in red cell membranes in nephropathy are similar to those seen during activation of lipid peroxidation in membranes. The possibility of lipid peroxidation involvement into the pathogenesis of nephropathy is discussed.