A method is proposed for estimation of the binding constants B of solutes to a counter-ion of cation-exchange resins from their apparent distribution coefficients onto resins with different divinylbenzene contents. The method can be modified,when the B value of a solute is zero. The methods were applied for estimation of the B values of glucose, mannose, fructose, galactose, and sorbose to the sodium ion at 25 degrees C. Assuming that the B value of glucose is zero and using the modified method, the B values of mannose, fructose, galactose and sorbose are evaluated.