A great deal of effort has been put into perfecting preservation of red blood cells for transfusion. A simple solution of citrate, phosphate and dextrose (CPD) can be used to preserve red cells, but inclusion of additives (adenine, mannitol, etc.) will further extend the shelf-life of red blood cells. Currently, the effectiveness of a red cell preservative is determined by the amount of in vitro hemolysis prior to transfusion and then in vivo recovery the red cells after transfusion. However, simply assessing the survival of red cells does not provide information about the effectiveness of transfused red cells to function (i.e. deliver oxygen to tissues). This program will review the functional ability of transfused red cells that can be determined by a number of measures such as diphosphoglycerate (DPG), adenosine triphosphate (ATP) and nitrous oxide (NO) content. In addition, it will address future guidelines defining the acceptability criteria for preservative solutions that may include both measures of red cell survival and functional quality.