Lipid peroxidation in biological membranes was studied in healthy individuals under emotional stress and in patients with neurosis. The plasma levels of malonic dialdehyde (one of the end products of peroxidation) directly correlated with the severity of emotional stress. Patients with neurotic disturbances showed activation of peroxidation expressed in increase of its initial and end products and decreased levels of alpha-tocopherol. A relationship has been found between clinical characteristics of patients and intensity of the studied biological processes. A conclusion is drawn about the involvement of lipid peroxidation in the pathogenetic chain responsible for the development of neurotic symptom complex.