Rapid and accurate diagnosis is very important for the control of influenza, which is usually diagnosed on a clinical basis. Recently, some rapid diagnostic tests for detecting influenza viruses in respiratory specimens have become available and have proved to be clinically useful. The rapid confirmation of an influenza diagnosis enables prompt treatment with specific antiviral drugs and also decreases the use of unnecessary antibiotics. The rapid tests are also useful for detection of institutional influenza activity. It is important to understand the performance characteristics of the rapid tests.