Molecular methods like the Polymerase Chain Reaction (PCR) are substantial parts of veterinary diagnostics especially in poultry production. The Real Time PCR, for example, offers the possibility to test for and certify the presence of Avian Influenza Virus in acute disease outbreaks within only a few hours. As such, this has become an essential part of disease control. While the detection of antibodies would only lead to retrospective information on the health status of a flock, the PCR offers the most current information, e.g. about the freedom of Mycoplasma. In addition to that, today’s PCR and subsequent sequencing process offer a fast characterization of Bronchitis field strains or the analysis of virulence genes in E. coli isolates.