A method for testing the identity of several antigens using an Ouchterlony plate, a glass plate covered with a thin layer of agar on which is incised a hole surrounded by several other holes that serve as wells. In the central well is placed an antibody, and the antigens in question are placed in the surrounding wells; the antibody and antigens diffuse towards each other until they meet and form a visible precipitin line. An antigen in an adjacent well forms a precipitin line that is continuous with the first only if the two antigens are identical. Similarly, the plate can be used to test the identity of antibodies against a single antigen in the central well.