The equilibrium distribution coefficients (p-value) of D-arabinose between the water in sulfonate ion-exchange resin and the external aqueous solution vary with the nature of the five alkali metal counterions studied. The strongest exclusion (lowest p-value) is found in the Li+ resin and the least exclusion (highest p-value) in the Cs+ resin. The p-value decreases with the increasing atomic weights for the alkali-metal ions: pCs+ greater than or equal to pRb+ greater than or equal to pRb+

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... r than or equal to pK+ greater than pNa+ greater than pLi+. The water contents of these resins, on the other hand, vary in the opposite direction, being highest for the Li+ resin and lowest for the Cs+ resin. These data disprove the pore size theory but fully substantiate the predictions of the association-induction hypothesis.