To differentiate between rRT-PCR inhibition due to the presence of inhibitors in the RNA after extraction and variation due to differences in efficiency of extraction, 23 RNA extracts from samples with inhibitors were spiked with two concentrations of purified CoxB3 enterovirus RNA (Fig. 2 ). The first concentration was equivalent to that of MS2 (R 1 , equivalent) and the second contained 64 fold (6 Cts) more enterovirus RNA (R 2 , high). No significant difference between inhibition of MS2 rRT-PCR and enterovirus rRT-PCR was noted when equivalent amounts of enterovirus RNA was added to extracts prepared by protocols A, B and C (Fig. 2. part 2) . However, when the higher amount of enterovirus RNA was added, there was significantly less inhibition of enterovirus rRT-PCR than MS2 rRT-PCR extracts prepared using protocols B, C, and D, but not A. Thus, the decrease in MS2 rRT-PCR can serve as a measure of the amount of inhibitors in the RNA extracted by each of the extraction protocol.