A multiplex quantitative reverse transcription-polymerase chain reaction–enzyme hybridization assay (Hexaplex; Prodesse, Milwaukee) was developed and used to rapidly detect and quantitate RNA of respiratory syncytial viruses A and B, influenza viruses A and B, and human parainfluenza virus types 1, 2, and 3 in nasal wash specimens in a single test. Primers and probes originated from highly conserved regions of each viral genome. Six and a half primer pairs were mixed for the simultaneous detection and quantitation of RNA from seven different respiratory viruses. We tested 109 clinical samples with this assay. Twenty-nine virus culture-positive samples were all positive by Hexaplex. Samples from 40 symptomatic patients were negative by virus culture, but eight of these were positive by Hexaplex. Forty samples from asymptomatic children were negative by both virus culture and Hexaplex. No cross-reactions were noted among 17 different respiratory viruses with use of this assay. Hexaplex was 100% sensitive (95% confidence interval [CI], 0.88–1.0) and 98% specific (95% CI, 0.97–0.99). All eight “false-positive” Hexaplex results (in comparison with negative viral culture results) were for symptomatic patients with low numbers of virus RNA copies. This finding suggests that Hexaplex may be more sensitive than virus culture. Our data demonstrate that Hexaplex is a rapid, sensitive, and specific quantitative test for the diagnosis of infections with these seven common respiratory viruses.