During one phase of the study, 14 healthy human volunteers will donate a unit of Packed Red Blood Cells (PRBC), which will be leukoreduced and stored in Additive Solutions-1 (AS-1), and then transfused back to the subjects after 3 days of storage at 4º C in the MGH Blood Bank (Fresh Blood arm). The second part of the study consists in the collection of another unit of PRBC from the same volunteers which will be transfused back to them after 40 days of storage (Old Blood arm). Finally in the third part, like in the second one, one unit of PRBC will be withdraw and stored for 40 days, but 80 ppm (parts per million by volume) Nitric Oxide in air will be administered together with the transfusion. There will be a 2 weeks interval after each PRBC transfusion.