Blood donors to the National Institutes of Health's Department of Transfusion Medicine (blood bank) will have their blood screened with transcription mediated amplification, a type of NAT test. Donors whose blood is found positive for HIV or HCV by NAT testing will be notified and asked to participate in this study. Those who agree will provide a blood sample about once a week for 3 months. The samples will be tested with additional assays to detect evidence of HIV or HCV infection. If the test results are confirmed positive, no more blood samples will be collected. The results of the tests and their significance will be explained to participants.