Equilibrium dialysis is used to investigate the binding of chromate anions to the cationic polyelectrolyte, poly(diallyldimethylammonium chloride), in the presence and in the absence of added sodium chloride. The binding of chromate to the polyelectrolyte is predicted by using a model which combines thermodynamic relations with the Oosawa two-state polyelectrolyte theory. Allowances are made for the nonideality of the bulk aqueous phase by introducing ion activities and ion activity coefficients. The model quite successfully accounts for the experimental data when the theoretical value of a potential parameter is utilized and when the fraction of the apparent volume containing the bound counterions is determined by considering the dimensions of the bound chromate ions.