High-throughput multiplex assays for respiratory viruses are an important step forward in diagnostic virology. We compared one such assay, the PLx Multi-Code Respiratory Virus Panel (PLx-RVP), manufactured by Eragen Biosciences, Inc. (Madison, WI), with conventional virologic testing, consisting of fluorescent-antibody staining plus testing with the R-mix system and fibroblast tube cultures. The test set consisted of 410 archived respiratory specimens, mostly nasopharyngeal swabs, including 210 that had been positive by conventional testing for a balanced selection of common respiratory viruses. Specimens yielding discrepant results were evaluated using a panel of respiratory virus PCR assays developed, characterized, and validated with clinical specimens. PLx-RVP increased the total rate of detection of viruses by 35.8%, and there was a 25.7% increase in the rate of detection of positive specimens. Reference PCR assay results corroborated the PLx-RVP result for 54 (82%) of 66 discrepancies with conventional testing. Of the 12 specimens with discrepancies between PLx-RVp and the reference PCRs, 6 were positive for rhinovirus by PLx-RVP and the presence of rhinovirus was confirmed by nucleotide sequencing. The remaining six specimens included five in which the PLx-RVP failed to detect parainfluenza virus and one in which the detection of influenza A virus by PLx-RVP could not be confirmed by the reference PCR. Taking the results of the reference PCR assay results into account, the sensitivities of the PLx-RVP for individual viruses ranged from 94 to 100% and the specificities ranged from 99 to 100%. We conclude that PLx-RVP is a highly accurate system for the detection of respiratory viruses and significantly improves the rate of detection of these viruses compared to that by conventional virologic testing.