We performed virus isolation tests for respiratory viruses on combined nasal wash-throat swab specimens collected from infants and children with acute respiratory illnesses presenting to a hospital clinic during a 3-month period of concurrent epidemics of respiratory syncytial virus (RSV) and influenza A virus (Flu A) infections. Virus isolation results were used to assess the utility of commercially available rapid diagnostic kits for these two viruses. The kits employed direct immunofluorescence (IF) of cells (Imagen for RSV and Flu A), indirect IF of cells (Baxter Bartels Microscan), and enzyme immunoassay (EIA) (Becton Dickinson Directigen for RSV and Flu A and Abbott TestPack for RSV). All testing was completed on 81 specimens from 80 subjects. Of the 81 specimens, 53 (65%) yielded a virus: RSV, 28%; Flu A, 25%; rhinovirus, 6%; and enterovirus, cytomegalovirus, herpes simplex virus, and adenovirus, 2 to 4% each. Among the tests, Bartels Microscan and Directigen Flu-A exhibited the highest sensitivities (87 and 75%) and efficiencies (94 and 94%) for RSV and Flu A, respectively. All the tests exhibited high specificity. Thus, optimal detection of RSV and Flu A among infants and children who presented to a hospital clinic required two different detection methods (IF and enzyme immunoassay) and kits from two different companies (Baxter [Bartels Microscan] and Becton Dickinson [Directigen]).