The interaction of alkyltrimethylammonium bromide (C(n)TAB) with sodium (carboxymethyl)cellulose (NaCMC) in dilute aqueous solutions is investigated. The effect of stilt on the binding to NaCMC of high linear charge density (xi = 3.0) is investigated using a surfactant-sensitive electrode and compared with the behavior in other polyelectrolyte systems. From time-resolved fluorescence quenching experiments the aggregation numbers for C(12)TAB and C(14)TAB micelles formed with NaCMC as counterion (no salt) are obtained as 58 and 83, respectively, i.e., close to the values for the corresponding polyelectrolyte free systems, The binding of C(12)TAB to NaCMC with different linear charge densities (xi = 0.8, 1.5, 2.0, 2.3, 3.0) is determined in the presence of 2.5 mM sodium bromide. From the binding isotherms, the critical aggregation concentration (cac) of the surfactant and the cooperativity in the binding are estimated. The cac decreases and the cooperativity increases with increasing charge density of the polyelectrolyte. The C(12)TAB aggregation number is found to increase from 43 in solutions of NaCMC with the lowest charge density to 62 in the one with the highest charge density. A comparison of the interaction between C(12)TAB and different polyelectrolytes under the same conditions suggests that a high aggregation number generally corresponds to a high cooperativity in the binding and vice versa. Some important aspects of the cooperative binding of surfactant to polyelectrolytes of opposite charge is illustrated in a law of mass action model, The model correctly predicts the observed relative increase in the cooperativity with increasing aggregation number and can qualitatively account fur the effect of salt on the cooperativity and the cac.