An optical immunoassay test, FLU OIA (BIOSTAR, USA), was evaluated for the diagnosis of influenza viral infection. The reactivity of the FLU OIA test was evaluated using 42 influenza strains (25 human influenza A, 12 human influenza B, 2 swine influenza A and 3 avian influenza A strains). The FLU OIA test showed positive results for all influenza strains. There was no evidence that cross-reactivity occurred with non-influenza viruses. The detection limit of the FLU OIA test was found to be 3.0-6.5 x 10(4) pfu/assay for human influenza A and B strains. The sensitivity and specificity of the FLU OIA test compared to isolation in cell culture was 89.7% and 76.0% for testing of 54 nasopharyngeal aspirate specimens. The FLU OIA test is rapid and easy for the detection of influenza A and B viral antigen and provide a valuable tool for the rapid diagnosis of influenza viral infection.