Binding competition assays. Binding competition assays can be used to assess if the epitopes of two different antibodies are in close proximity to each other, or possibly identical. First, one antibody is allowed to bind under saturating conditions. Second, the other antibody is added to see if it can bind as well. The illustration here depicts a standard ELISA, but this can also be executed with a sandwich ELISA format. When antibodies compete for the same region of the antigen, the presence of the first antibody precludes binding of the second. In contrast, noncompetitive antibodies can both bind because the epitopes are far enough apart.