During the process of storing erythrocyte-containing blood products, components of the preservatives and modifications of the erythrocyte function cause disorders of the electrolyte and acid-base balance as well as a deficiency of 2,3-diphosphoglycerate (2,3-DPG). Thereby transitory hyperkalemias may occur in the course of a massive transfusion, if the patient has a shock or another disturbance of the regulating mechanisms caused by diabetes mellitus or a treatment with β-blockers or ACE inhibitors. During the treatment with blood components, hypocalcemia and hypomagnesemia may develop after a dose of more than 12 fresh frozen plasms (FFP) per hour, if the metabolism of citrate, which binds bivalent cations as a chelate, is disturbed by hypothermia, shock or during the anhepatic stage of a liver transplantation. As a consequence, a low-output syndrome as well as tachyarrhythmias and torsades de pointes may develop. Whether the decrease of the 2,3-DPG level with the accompanying leftward shift of the oxyhemoglobin dissociation curve brings about a deficiency of the oxygen supply of the organs, has not yet been verified by experiment. The studies presented rather point at morphological changes of the erythrocytes due to the storage as the cause of the disturbances of capillary perfusion. For this reason patients with impending organ failure or marked disturbances of the coronary or cerebral perfusion should be transfused with packed red blood cells (RBCs) not older than 14 days.