Abstract: A method of comparing the binding strengths of a plurality of different ligands to a receptor, in which several micro-cantilever structures (10) are coated with the receptor on at least a part of a surface (13) of each micro-cantilever structure (10). Each micro-cantilever structure (10) is then contacted with a different ligand solution, and the amounts by which the micro-cantilever structures deflect are compared. The deflection may be detected by an optical lever (16,18; 28). The micro-cantilever structures (10) may be in the form of an array, each structure (10) being in a respective well (24), to which ligand solutions are added.