Light-scattering studies of the structure of macromolecular complexes formed between poly(ethylene oxide) [PEO] and a cationic surfactant, hexadecyltrimethylammonium chloride [HTAC], in aqueous solution, are reported. Analysis of the angle dependence of the scattered intensity indicates that binding of HTAC micelles is accompanied by an increase in radius of gyration (R-g), up to the maximum binding point. From measurements of the molecular weight of the PEO-HTAC complex, accounting fur preferential binding of surfactant, we deduce that, at the maximum binding condition, 0.12 mol of HTAC is bound per mol of EO. In addition, evaluation of the PEO molecular weight, using equilibrium dialysis, indicates approximately 2.0 +/-0.3 PEO chains are incorporated in the complex. Beyond maximum binding, electrostatic screening induces the PEO chain to contract, evidenced by a reduction in R-g. Measurements of R-g at the maximum binding point for three different PEO molecular weights indicate that the relative chain expansion is comparable, R-g,R-complex/R-g,R-PEO similar to 1.9 The results provide insight into earlier observations of a viscosity maximum, when titrating dilute solutions of PEO with HTAC.