Currently used systems for red blood cell (RBC) collection and storage for transfusion have the disadvantage that the RBC 2,3-bisphosphoglycerate (BPG) concentration is depleted within two weeks of storage, resulting in a left-shift of the oxygen dissociation curve and a temporarily impaired capacity to deliver oxygen. We have studied the effects on red cell metabolism, morphology and in vivo recovery of 49-day storage of RBC, with collection in half-strength citrate CPD (0.5CPD) and storage in an additive solution containing citrate, adenine, mannitol, phosphate and glucose (RAS2). Traditional CPD-SAGM was used for comparison. Component preparation was performed after an initial holding period of the whole blood at ambient temperature for 8h. The BPG concentration in 0.5CPD-RAS2 RBC was 0.633±0.120 mol (mol Hb)^-1 as compared to 0.454±0.138 mol (mol Hb)^-1 in CPD-SAGM RBC which implied a decrease to 67 and 48% of normal concentration, respectively. The mean RBC BPG concentration was maintained at the initial level for 28 days in the new system but decreased to very low levels within 14 days in the controls. The total adenine nucleotides were well maintained in both systems, adenosine triphosphate slightly better in the new system. Hemolysis after 49 days was 0.35±0.21% in the new system and 0.72±0.25% in the controls (p<0.001). The morphology was better maintained in the new system (p<0.001). The 24-hour posttransfusion survival of 49-day stored RBC was 78.9±7.1%. The membrane leakage of sodium and potassium was not significantly different in the two systems. The concentration of inorganic phosphate (Pi) in the extracellular fluid of 0.5 CPD-RAS2 RBC was initially 7.1±0.8 mmol l^-1. It decreased to approximately 5.5 mmol l^-1 during the first 2 weeks of storage and then slowly increased to 9.4±0.9 mmol l^-1 on day 49. Pi in the CPD-SAGM controls was low initially but rose to 6.2±0.4 mmol l^-1 at the end of storage. The new system offers clearcut advantages as compared to traditional systems and does not seem to raise any serious clinical objections against its use even in massive transfusions.