A rapid enzyme immunoassay membrane test, Directigen Flu A (Becton Dickinson, USA), was evaluated by using virus isolates and clinical specimens. The reference laboratory diagnosis was based on the results of virus isolation. Directigen Flu A was reactive for all subtypes of human influenza A viruses, including reference strains of H1N1, H2N2 and H3N2. Moreover, H5N1 (Hongkong/156/97) was also detected by this kit. No cross reactivity was detected with other respiratory viruses. Directigen Flu A showed positive reaction with the solution containing influenza A virus of 2.4 x 10(3) pfu/assay. The rapid test demonstrated 77.9% sensitivity and 98.4% specificity for testing of throat swabs from children with respiratory symptoms. It showed higher sensitivity and specificity (92.1% and 100%) for testing of nasopharyngeal aspirates. Directigen Flu A should be useful for the rapid diagnosis of influenza A virus infection.