Immunologic testing in veterinary medicine is primarily used to diagnose exposure to microbes by measuring antibodies in serum, commonly known as serology. Numerous methodologies, including agglutination tests, neutralization tests, and enzyme-linked immunosorbent assays (ELISA), are principal tests commonly used to identify and quantitate pathogen-specific antibodies. They serve different purposes and provide unique information concerning the immune response of animals. Antigen capture ELISAs have more limited use in the diagnosis of some infections, such as bovine viral diarrhea virus (BVDV) and Mycobacterium bovis. Collectively, these tests form the typical panel of probes to investigate animal infections and are commonly offered together in commercial and government laboratories.