Immunoprecipitation - When correct conditions are employed, antigen and antibody react to form a precipitate. This precipitation phenomenon has been used to separate and purify enzymes and other antigenic substances in a variety of ways.

One application of immunoprecipitation is immunoelectrophoresis. This is the most sensitive method for the detection of enzymes and antigens in a mixture. It involves combination of elcctrophoresis and gel diffusion.

In this procedure, the mixture containing the enzyme (or antigen) is placed in a small well, made in a layer of agar placed on a glass sheet, or a microscopic slide. It is then subjected to electrophoresis by application of an electric current. The enzyme and other components of the mixture migrate through the agar at variable rates.