The drugs which are foreign to the organism can increase the production of free oxygen radicals either spontaneously or by means of metabolic activation, or they can act as inhibitors of protective enzymic systems. They can thus activate the process of peroxidation of lipids (LPO) causing gradual structural degradation of biomembranes, thus negatively affecting the course of both pathological and physiological processes in the organism. Investigation of the inductive or inhibitory effect of newly developed drugs on LPO should become a part of their preclinical and clinical testing. The present paper proposes and recommends on the basis of the present authors' results the methodical approaches to the investigation of LPO processes.