Legionella pneumophila is the causative species in most cases of Legionnaires' disease (LD). CDC scientists have developed a real-time PCR assay capable of detecting all Legionella species and discriminating L. pneumophila from other Legionella species. LD is typically difficult to diagnose from a clinical standpoint as it confers no unique clinical features or symptoms. This assay provides a rapid and accurate alternative to laborious PCR assays, prone to aberrant results. It provides a sensitive alternative for diagnosis of Legionnaires' disease and detection of L. pneumophila.