SummaryIt has been shown in this study that the selenium (Se) content and glutathione peroxidase (GSH-Px) activity in blood and tissues of Keshan disease (KD) patients were lower than those of control subjects. Also these patients showed abnormal lipid composition of plasma and of membranes of erythrocytes and myocardium, such as a decrease in phospholipid (PL) and in cardiolipin (CL) and an increase in the molar ratio of cholesterol/PL and of sphingomyelin/phosphatidylcholine. In addition the cytochrome c oxidase (CCO) activity in their myocardial mitochondria was decreased.A guinea pig model fed cereals from Yunnan, a KD-endemic area, for 15 weeks, showed a series of changes similar to those observed in KD patients, as above, such as decreases in Se level and activity of GSH-Px and of glutathione-S-transferase, and significant increases in lipid peroxides, hydroperoxides (conjugated dienes), and fluorescent chromolipids. The lipid composition of myocardial mitochondria in the animal model was abnormal; especially, the CL was decreased. Even though the CCO content was almost unchanged, activity of the enzyme was decreased remarkably. This result coincides exactly with the changes seen in the circular dichroism spectra of myocardial mitochondria, the peak values (208 and 224 nm) of which were lower significantly than those of the control.