In order to narrow the infectious period (window) between the time of viral exposure and the time a virus can be serologically detected, blood centers throughout the United States are implementing nucleic acid testing (NAT) for HIV and HCV. Early studies have shown that NAT testing can significantly narrow the infectious window, particularly for HCV. There is the potential that NAT testing could completely eradicate the transfusion risk of HIV and HCV. The test is thus likely to add substantially to the safety of blood transfusions and, although not licensed, has been implemented by all blood suppliers and transfusion services in the United States. NAT testing is currently being used under an IND mechanism. The IND stipulates that blood donors need to be informed through a supplemental information packet that such testing is being performed and that if found positive they may be recalled for additional testing. At the time of recall, an IRB approved study-specific informed consent is administered and additional tests are performed to verify the initial NAT result. The Department of Transfusion medicine is participating in this national validation of NAT testing and will provide donor samples for centralized testing and statistical reporting to FDA. The potential benefits of this testing for blood safety are great and the risk to donors is considered minimal. Not seeking subjects for enrollment.