Immunological techniques make use of the interaction of antigen and antibodies. Antigen is any foreign molecule which can elicit an immune reaction in the body. Antibody which is specific to antigen will be produced and it reacts to form antigen-antibody complex.

The Ouchterlony immunodiffusion can be used to quantify antibodies / antigen in the given sample.In Ouchterlony double immunodiffusion, double refers to the diffusion of both antigens and antibodies. In this diffusion methiod, test antigen and antibody diffuse toward each other in a semisolid medium to a point in the medium where optimum concentration of each is reached. A precipitation line or band is formed where the antigen-antibody complex is formed.

 Ouchterlony Double Diffusion

The Ouchterlony test method involves making an agarose gel in a petriplate on to which wells are made using a cork borer. Antigen or antibody are added to the respective wells and incubated the plate for 24-48^oC at room temperature.When homologous antigen and antibody diffuse toward each other from the individual wells, a precipitin line will form somewhere between the two wells.

Based on the precipitation line amount of test antigen/antibody can be found out.