This study will enroll normal healthy volunteers between 18 to 50 years of age. 500 ml (1.0 unit) of blood will be collected from subjects who will then return in 5-10 days and be re-infused with the blood 5-10 days after storage.The subjects will return after 25-37 days and be infused with blood 35-42 days after storage. The study will use a tool called strain gauge plethysmography and the drug acetylcholine to measure the effect of fresh (i.e., 5-10 days) versus aged (35-42 days) autologous blood transfusions on forearm blood flow in healthy volunteers.