Oxidative stress mediates damage to various cells and is thought to be involved in various pathologies, including hereditary and acquired hemolytic anemias. It is induced by a multitude of physiological and environmental factors, including extracorporeal manipulation of blood. As a result, hemodialysis induces oxidative damage to red blood cells, thereby increasing their susceptibility to hemolysis and shortening their life span. We studied the effect of apheresis on the oxidative status of blood components. Using flow cytometric measurements, we showed that red blood cells, lymphocytes, monocytes, and polymorphonuclear cells undergo oxidative stress induced by the procedure. Their reactive oxygen species and externalization of phosphatidylserine increased, while their levels of reduced glutathione decreased. This oxidative stress, which may be caused by a direct interaction with the membranous system, may lead to cellular abnormalities with clinical consequences such as hemolysis and platelet hyperactivation.