During the past 2 years, Citrate-Phosphate-Dextrose (CPD) blood preservative solution has largely replaced Acid-Citrate-Dextrose (ACD) solution in most blood banks, partly because of the superior preservation of diphosphoglycerate levels (2,3 DPG) and oxygen transport of red cells stored in CPD solution. Although superiorin vitromaintenance of oxygen transport capabilities is established, fewin vivocomparative studies have been done.Forty-four trauma patients were studied who had 90% or more of their estimated blood volume replaced acutely: 24 patients received blood preserved in ACD solution; 20 received blood preserved in CPD solution. Samples were obtained immediately after transfusion and then daily. Values of P50and 2,3 DPG were adjusted for covariance on mean age of transfused blood.The relationship between P50and 2,3 DPG was significant acutely and at 24 hours in ACD-transfused patients (r=0.91,p<0.01;r=0.856,p<.01). The relationship between P50and 2,3 DPG was not significant acutely, but was at 24 hours in CPD-transfused patients (r=0.67,p<0.10;r=0.74,p<0.01). Comparison between patients transfused with ACD and CPD by P50, 2,3 DPG, and length of storage was not significant.When massive transfusion of blood products is required, the ability of blood banks to provide transfusion components will determine the shelf-life, and therefore the oxygen transport capability, of the blood administered. Whether resuscitation with blood of advanced shelf-life is deleterious could not be determined from this retrospective study. Although no practical superiority of CPD over ACD could be demonstrated,in vitrostudies clearly demonstrate CPD to be superior to ACD solution in maintenance of 2,3 DPG values. The present study is not intended to justify continuance of ACD as a preservative. It suggests that the small preservative advantage of CPD over ACD will probably eventually result in the development of a solution superior to ACD and CPD.