The long term goal is to extend the storage shelf life of human red cells (RBC) with improved in vivo survival. An additive-preservative solution containing ammonium (NH4+) and phosphate (Pi) ions in addition to adenine, glucose, and mannitol has been shown to maintain adenosine triphosphate (ATP) levels of RBC high enough for more than 12 weeks at 4 to suggest good in vivo RBC survivals. The aims are to find the survival studies to establish the maximum storage interval compatible with acceptable posttransfusion survival; to perform metabolic studies to establish the biochemical pathways involved in the maintenance of high ATP concentrations under these conditions. Metabolic studies are designed to determine whether increased synthesis of AMP or its decreased degradation of both occur. The role of phosphofructokinase activity will also be explored. Preliminary data indicate a strong possibility that satisfactory storage of RBC for 12 or more weeks can be achieved. The resulting blood donor programs; conservation of the blood supply by decreased loss through outdating; and decreasing the usage of blood and the rate of tissue iron accumulation in chronically transfused patients because of the longer in vivo survival of better preserved RBC.