Effects of linoleic acid and its oxidation products (with 75--80% content of hydroperoxide) on rat liver mitochondria were studied by polarographic and spectrophotometric methods. Both agents according to their concentration are able to uncouple oxidation and phosphorylation and to inhibit the electron transport in the initial region of the respiration chain as well. Unlike the unoxidized linoleic acid, its oxidation products increase the activity of some enzymatic systems of mitochondria, and at high concentrations they produce a more pronounced effect on the electron transport.