Equilibrium dialysis is a specificapplication of dialysis that isimportant for the study of thebinding of small molecules andions by proteins. It is one of sev-eral methods available for thispurpose, and its attractive fea-ture continues to be its physicalsimplicity. Another attractive fea-ture of equilibrium dialysis is theability to perform interactionstudies without the use of fluo-rescent or radiolabeled tags.Generally, the objective of an equilibrium dialysis experiment is tomeasure the amount of a ligand bound to a macromolecule. This istypically done through an indirect process because in any mixture ofthe ligand and macromolecule, it is difficult to distinguish betweenthe bound and free ligand. If, however, the free ligand can be dia-lyzed through a membrane, until its concentration across the mem-brane is at equilibrium, the free ligand concentration can be meas-ured easily. Data obtained under different experimental conditionsthen provides information on various binding parameters of the com-pounds such as the binding constants and the number of binding sitesor binding capacity.