A reduction in the glutathion peroxidase (GSH-Px) activity of the blood and myocardium accompanied with an increase in the leukotriene C₄(LTC₄), free radicals and lipid peroxides (LPO) concentrations of the plasma and myocardium are found in Wistar rats fed with the low selenium (Se) and vitamin E (VE) grains from a Keshan disease (KD) endemic area for 11 weeks. The concentrations of LTC₄, free radical and LPO were decreased in these rats and the GSH-Px activity is strengthened except the group supplemented with VE alone. These results suggest that the dietary deficiencies of Se and VE might take part in the occurrence and development process of myocardial damage in KD and other ischemic and anoxic cardiomyopathy by affecting the activity of lipoxygenase in arachidonic acid metabolism and by accelerating the synthesis of LTC₄ owing to excessive free radicals and LPO.