Abstract: The present invention describes peptides capable of specifically binding to preselected micromolecules or to their natural receptor. The preselected molecules include but are not limited to drugs, vitamins, neuromediators and steroid hormones. Methods of using the phage display libraries to identify peptide compositions in preselected binding interactions are also disclosed. The retrieved peptides mimicking a natural receptor binding site to preselected molecules are used as is or as ligands to re-screen the same or different libraries to find and/or derive new receptor ligands, or are used to elicit the production of antibodies capable of binding to the natural receptor. The two categories of effector molecules (peptides or antibodies) may find diagnostic, therapeutic or prophylactic uses. The peptides directly derived from the phage display libraries may be used as drug detectors or antidotes.