Stroke-prone spontaneously hypertensive rats (SHRSP) were kept on a 1% NaCl solution as drinking water to shorten the onset-time of a stroke. The level of lipoperoxide (LPO) in the erythrocytes of SHRSP loaded with salt for 22 days was significantly higher than that of the controls. Idebenone treatment (30 mg/kg per day, p.o.) markedly decreased the LPO to the level of the controls. Hemolysis in SHRSP was accelerated by the salt-loading. Idebenone significantly inhibited the hemolysis in a dose-dependent manner. These results suggest that idebenone inhibits lipid peroxidation in erythrocytes and stabilizes the erythrocyte membrane.