Murine monoclonal antibodies directed against type-specific antigens of influenza A and B viruses have been shown to be useful diagnostic reagents for the detection of influenza viruses by immunofluorescence testing of nasopharyngeal cells. We have developed fluorescent focus assays utilizing these antibodies in cell culture chamber slides and shell vials for the rapid diagnosis of influenza A and B. Chamber slide assays were compared with virus isolation in 160 specimens from 135 patients with symptoms of influenza. Virus isolation was compared with immunofluorescence testing in 38 of the 160 specimens. Compared with virus isolation, 24-h cell culture chamber slide assays had a sensitivity of 75% and a specificity of 96%. Immunofluorescence testing of nasopharyngeal cells was only 38% sensitive and 91% specific. Shell vial assays were compared with virus isolation for 89 specimens. At 16 to 18 h postinoculation, the shell vial assay was 84% sensitive and 100% specific. We conclude that both chamber slide and shell vial assays are rapid, sensitive, and specific techniques for the diagnosis of influenza.