A mass transport theory of the gel chromatographic procedure of Hummel and Dreyer for measuring the binding of small ligand molecules to macromolecules has been formulated for ligand-mediated macromolecular association. It is concluded that the Hummel-Dreyer procedure is the method of choice for quantitating ligand binding in such systems. Guidelines are drawn for unambiguous interpretation of the nonclasical elution profiles in terms of the number of binding sites on the macromonomer and their intrinsic binding constant. Most of these guidelines also apply to static equilibrium methods such as equilibrium dialysis.