BACKGROUND: An HIV-1 and HCV NAT blood screening assay (Procleix HIV-1/HCV, Gen-Probe, Inc.) simultaneously detecting HIV-1 and HCV RNA) has been implemented. Donor plasma samples reactive in the Procleix HIV-1/HCV assay are tested with the HIV-1 and HCV discriminatory assays to resolve whether HIV-1 RNA, HCV RNA, or both are present. STUDY DESIGN AND METHODS: To determine the specificity of the Procleix HIV-1/HCV assay, data were analyzed for samples from 192,288 donations, tested in 16-member pools. To determine sensitivity, data were analyzed for 2014 commercial samples known to contain HIV-1, HCV, or both, as well as 10 HIV-1 and 10 HCV commercial seroconversion panels. RESULTS: The specificity of the Procleix HIV-1/HCV assay was 99.7 percent. The HIV-1 and HCV discriminatory assays showed similar specificity. The sensitivity of the Procleix HIV-1/HCV assay was 99.9, 99.6, and 100 percent, respectively, for samples containing HIV-1, HCV, or both. The Procleix discriminatory assays were comparably sensitive. The Procleix discriminatory assays detected all tested samples of known HIV-1 subtype or HCV genotype. Procleix HIV-1/HCV testing of seroconversion panels showed that the median times to a positive reaction for HIV-1 and HCV were reduced by 3 and 25 days, respectively, compared to serologic tests. CONCLUSION: These studies support the use of the Procleix HIV-1/HCV assay for routine blood donor screening.