The present invention relates to a method for identifying a binding agent or epitope for use in drug design, drug targeting or diagnostics. The method employs contacting and sorting binding agents and cognate epitopes from collections thereof, characterizing the binding agent and cognate epitope, detecting the level or location of the epitope in a sample using the binding agent, and correlating the level or location of the epitope in the sample with the presence or stage of a disease or condition to identify novel drugs, targeting moieties, or diagnostic agents.