Addition of ionic surfactants to aqueous solutions of polyelectrolytes, having charge opposite to that of the added surfactant, can result in pronounced effects on the system viscosity and can lead to the formation of viscoelastic gels with useful technological applications. We report here the modulation of the rheological properties of such a polymer-surfactant system (JR400 cationic cellulose ether plus sodium dodecyl sulfate) via the addition of cyclodextrins. Cyclodextrins, cyclic oligomers of alpha-D-glucose, can form inclusion complexes with the hydrophobic moieties of surfactants. Thus they disrupt the (physically cross-linked) network formed by the oppositely charged surfactants and polymers, and they can counteract (and reverse completely) the viscosity enhancement caused by the surfactant. The apparent surfactant-CD stoichiometric ratio, obtained on the basis of rheological experiments in the polymer-surfactant-CD systems, falls between 1:1 and 1:2. The fact that this ratio is in the range expected for guest:CD-host complexes supports the notion that the observed viscosity reduction in the polymer-surfactant-CD system is primarily due to complex formation between the surfactant and CD. The present work is an example of how the molecular recognition abilities of cyclodextrin can be exploited in modifying the solution properties and functionality of polymers. Moreover, cyclodextrins can aid in resolving fundamental issues concerning the relative contributions of hydrophobic and electrostatic interactions to the solution behavior of polymer-surfactant mixtures.