The interaction between poly(ethylene oxide) or poly (vinylpyrrolidone) and cesium and tetraalkylammonium (tetramethyl to tetrabutyl ammonium) dodecylsulfate has been investigated by means of electrical conductivity measurements to determine the critical aggregation concentration (cac) of the surfactants in the presence of polymer. The cac values were compared to the values of the critical micellization concentration (cmc) of the surfactants in the absence of polymer. The value of the cac/cmc ratio increased with the radius of the counterion in the sequence: Na+ < Cs+ < tetramethylammonium(+) < tetraethylammonium(+) = tetrapropylammonium(+) = tetrabutylammonium(+) = 1.0. This result indicates that the strength of the interaction decreases upon increasing counterion radius. For the last three tetraalkylammonium ions the value cac/cmc = 1 indicates the absence of interaction. The results are discussed in an attempt to gain a better understanding of the mechanism of formation of surfactant aggregates bound to water-soluble polymers such as poly(ethylene oxide) or poly(vinylpyrrolidone). (C) 2003 Elsevier Inc. All rights reserved.