The present invention relates to an improved method for drug discovery. In particular the present invention provides a method of identifying compounds capable of binding to a functional conformational state of a protein of interest or protein fragment thereof, said method comprising the steps of: (a) Binding a function-modifying antibody to the target protein of interest or a fragment thereof to provide an antibody-constrained protein or fragment, wherein the antibody has binding kinetics with the protein or fragment which are such that it has a low dissociation rate constant, (b) Providing a test compound which has a low molecular weight, (c) Evaluating whether the test compound of step b) binds the antibody constrained protein or fragment, and (d) Select a compound from step c) based on the ability to bind to the protein or fragment thereof.