To further evaluate the sensitivity of the selected primers, we used FDA/CBER panels (kindly provided by Dr. Stephen Kerby, FDA), consisting of various amounts of viruses spiked into ''normal'' human plasma, that are specifically developed and used for the evaluation of commercially licensed NAT assays. Table 2 summarizes the testing results for the selected primers against the target viruses. One out of four primer sets targeting HIV-1, NP3/4, could detect the subtype B HIV-1 RNA at the concentration of 50 copies/ml of human plasma. Two other HIV-1 specific primer sets (NP51/52 and NP170/171) detected the HIV-1 RNA at 100 copies/ml of plasma. The 4th primer set, NP175/174, (targeting the conserved pol region and containing degenerative nucleotides to support broader variant coverage) could detect the virus only at 500 viral genome copies/ml of plasma. HIV-2 RNA was detected with primer set NP86/87 at the concentration of 10 copies/ml and with the primer set NP76/77 at the concentration of 50 copies/ml. Another primer set (NP84/ 85) detected HIV-2 at 100 copies/ml. HBV (genotype A) DNA was detected with the primer set NP11/97 at 50 copies/ml and with NP94/100 at 100 copies/ml. The third HBV specific primer set (NP11/97-mod) detected HBV at 500 copies/ml of plasma. Both HCV specific primer sets targeting the viral 59NTR detected HCV RNA at the concentration of 10 copies/ml of plasma. Two of the WNV-specific primer sets (NP21/22, targeting E protein gene, and NP176/177, targeting NS5) detected WNV at 50 copies/ml and the third primer set (NP178/179, also targeting NS5) gave a positive signal at 100 copies/ml of plasma.