The ABC methodology involves the following steps.

1. The application of an unlabeled primary antibody onto the tissue section, which binds specifically to the target antigen. 
2. The application of a biotinylated secondary antibody, which attaches to the primary antibody and introduces biotin molecules at the site of antigen binding. 
3. Application of a complex of avidin and biotin horseradish peroxidase conjugate (ABC). Avidin binds strongly to biotin, forming a stable complex. 
4. Development of the peroxidase by using DAB or other chromogenic substrates. This reaction produces a colored label at the site of the antigen, allowing for its visualization under a microscope.