The use of influenza A virus-inducible reporter gene segments in detecting influenza A virus replication was investigated. The RNA polymerase I promoter/terminator cassette was used to express RNA transcripts encoding green fluorescence protein or firefly luciferase flanked by the untranslated regions of the influenza A/WSN/33 nucleoprotein (NP) segment. Reporter gene activity was detected after reconstitution of the influenza A virus polymerase complex from cDNA or after virus infection, and was influenza A virus-specific. Reporter gene activity could be detected as early as 6 h post-infection and was virus dose-dependent. Inhibitory effects of antibodies or amantadine could be detected and quantified rapidly, providing a means of not only identifying influenza A virus-specific replication, but also of determining the antigenic subtype as well as antiviral drug susceptibility. Induction of virus-specific reporter genes provides a rapid, sensitive method for detecting virus replication, quantifying virus titers and assessing antiviral sensitivity as well as antigenic subtype.