A technique for the separation of macromolecules from smaller molecules by placing them within a semi-permeable membrane, such as Cellophane, separating them from a large volume of water. Only the low-molecular-mass diffusible molecules cross the membrane and pass into the larger volume; the macromolecules are confined to their original space. Equilibrium dialysis is the technique of quantification of binding capacity and affinity by dialysis of a macromolecule against various concentrations of a ligand and subsequent measurement of the final concentrations of bound and free ligand within the dialysis chamber and free ligand outside it.