Antibodies against albumin migrate on electrophoresis into agarose gel containing albumin, producing zones of immunoprecipitate (ZIP) in the gel. The amount of antibody in the sample applied is directly proportional to the distance from the point of application (i.e., the gel surface) to the front of the ZIP. This method possesses advantages for antibody measurement over procedures such as radial immunodiffusion and rocket immunoelectrophoresis.