Lipid peroxidation (LPO) in the heart of adult (10-12 month) and old (22-25 month) Wistar male rats was investigated during immobilized stress. Immobilization of rats was accompanied by increasing the concentration of all studied LPO intermediates in the myocardium of both age groups. Accumulation of LPO products in old rat hearts was considerably higher than in adult ones. Dimethyl sulfoxide injection limited stress-induced stimulation of LPO. There were age related variations in efficiency of this antioxidant effect on the heart during immobilized stress.