We intended to evaluate the diagnostic usefulness of a multiplex reverse transcriptase- PCR (mRT-PCR) assay kit under dual priming oligonucleotide system (DPO) for the childhood acute respiratory tract infections. Two hundred nasopharyngeal aspirates were taken from children < or =5 yr old admitted due to acute respiratory infections in 2004. Direct fluorescent antibody (FA) assays were performed with fresh specimens; then, mRT-PCRs for the detection of 12 respiratory viruses (Seeplex RV detection kit, SeeGene, Seoul, Korea) were tested with frozen specimens. FA assays for five common respiratory viruses showed positive results in 66 patients (33.0%), while mRT-PCR detected causative viruses in 112 patients (56.0%), including 16 co-infected cases (8.0%). A total of 129 viruses were identified: respiratory syncytial virus A/B (38.0%/7.8%), influenza virus A/B (10.1%/5.4%), parainfluenza virus 1/2/3 (7.0%/3.1%/7.8%), coronavirus 229E or NL63 (6.2%), human metapneumovirus (4.7%), adenovirus (4.7%), rhinovirus (3.9%), and coronavirus OC43 (1.6%). DPO-based mRT-PCR was found as a sensitive tool for the detection of the viruses that cause childhood respiratory infections. Clinical significances of the agents detected by mRTPCR need further evaluations.