This technique also referred to as the Ouchterlony method, 
may be used to determine the relation ship between antigen 
and antibodies. 
Principle: Antibody dilutions and specific soluble antigens are 
placed in adjacent wells. If the well size and shape, distance 
between wells, temperature, and incubation time are optimal, 
these solutions diffuse out, bind to each other, cross-link, and 
form a visible precipitate at the point of equivalence 
perpendicular to the axis line between the wells the 
precipitation bands will be compared with a standard antigen. 
The precise location of the band depends on the 
concentration and rate of diffusion of antigen and antibody. In 
a condition of antibody excess, the band will be located nearer 
the antigen well. If two antigens are present in the solution 
that can be recognized by the antibody, two precipitin bands 
form independently. 
Antibodies associated with autoimmune disorders such as 
rheumatoid arthritis and systemic lupus erythematosus can be 
identified by double diffusion.