A method is proposed for determining ligand saturation curves for each participating oligomer of an associating protein system from measurements which must, in general, be carried out on equilibrating mixtures of oligomers. If there are N oligomers of a given protein, (P sub 1, P sub 2 ... P sub N) there will be at given ligand activity (L), a characteristic value for ligand binding to each (L sub 1, L sub 2 ... L sub N), and N independent relationships involving the L sub i will be required to determine them independently. (N-1) of these may be obtained by measuring the dependence of the N-1 equilibrium constants K sub j equals (P sub j)/(P) super J on ligand activity which will yield L sub j - jL sub 1. This can be done using sedimentation equilibrium techniques. The remaining relationship may be obtained by measuring average binding by equilibrium dialysis, using the K sub j and total protein concentration to characterize the distribution of species in solution. It is proposed to apply the method to fructose diphosphatase.