The ELISA method (Enzyme Linked Immuno-Sorbent Assay) is a technique used in biochemistry to determine if a certain substance--such as a specific cytokine or antigen--is present within a sample. It is sometimes abbreviated as "EIA."
This technique uses special antibodies that attach themselves to the substance. These antibodies generate a specific color. The amount of color indicates the amount of substance present. (Sometimes, the substance must be viewed under ultraviolet light for the antibodies to generate this color.)
Another set of antibodies are used to "capture" the substance. These antibodies adhere to both the substance and the testing container, thus holding the substance in place.
A more sophisticated and sensitive technique, the ELISPOT method, was derived from the ELISA techique.