Differences in extraction efficiency might be at least as important as inhibitors, as Hata et al. [25] showed by adding separate controls for both extraction and amplification. We performed a similar analysis by adding enterovirus RNA to RNA samples after extraction and intact enterovirus to suspensions before extraction. The inhibition of enterovirus rRT-PCR correlated with MS2 rRT-PCR inhibition. It is important to note that all four extraction protocols yielded equivalent amounts of enterovirus RNA from enterovirus added to suspensions where there was no inhibition of MS2 RNA rRT-PCR in the samples for equal starting and elution volumes. The pattern and amount of enterovirus rRT-PCR inhibition was similar for specific suspensions regardless of whether enterovirus was added before extraction or viral RNA added to the reaction mix after extraction. This implies that the apparent decrease in the amount of MS2 RNA in an RNA extract where MS2 RNA was added to the lysis buffer was primarily due to failure to remove inhibitors present in particular stool suspensions.