The present invention relates to compositions and methods for screening, identifying, or selecting active compounds against a target protein using peptides derived from said target protein's active site(s) and functional antibodies active on said target protein active site(s). The invention also relates to the use of these peptides and functional antibodies for screening, identifying or selecting biologically active compounds. The invention also concerns a kit for implementing the above methods. The target protein is preferably a G-protein-coupled receptor (GPCR), and the invention can be used to identify compounds that are suitable for use in various areas, such as the pharmaceutical, agri-food and cosmetic industries.