The interaction between octaethylene glycol mono-n-dodecyl ether (C(12)E(8)) and ethylhydroxyethyl cellulose (EHEC) in aqueous solution has been studied by measuring the C(12)E(8) self-diffusion coefficient in the presence of EHEC at 25 degrees C. Micelle diffusion is influenced by the polymer in two ways, i.e. obstruction due to the polymer network and association of micelles to the polymer chains. It is demonstrated that, from studies using polymers of different polarity, a separation between obstruction and association effects can be achieved. It is found that the interaction between a relatively hydrophobic EHEC and the surfactant is dominated by a strong attraction leading to a formation of polymer-surfactant complexes. This observation is consistent with phase diagram findings. Taking into account the obstruction from both micelles and polymer chains, the binding isotherm of C(12)E(8) to the hydrophobic EHEC is calculated by using a two-site model.