The Enzyme Linked Immunosorbent Assay, or ELISA, is a popular laboratory technique for detecting the presence of specific chemicals in a sample, such as hormones, viruses, and bacteria. The procedure begins with coating a plate with antibodies that bind to the desired substance, followed by adding the sample to the plate. The substance will bind to the antibodies if it is present in the sample. The plate is then washed to remove any unbound material before adding a secondary antibody linked to an enzyme. This second antibody will bind to the substance-antibody complex, causing a detectable signal to be produced. ELISA is a sensitive and specific technique that is useful in medical research and diagnostics.