The interaction between ethyl(hydroxyethyl)cellulose EHEC and ionic surfactants has been studied in dilute solutions using titration microcalorimetry supplemented by viscosity measurements. Two EHEC samples of different hydrophobicity, as indicated by the differing clouding temperatures of 35 and 65 degrees C, were used. The surfactants studied were SDS, alkyltrimethylammonium halides RTAX with R equal to C-12, C-14, and C-16 and X either Br or Cl, and dodecylammonium chloride. The results are compared with results from measurements on dilute PEO solutions. The critical aggregation concentration cac, the saturation concentration C-2, and the amount of polymer-bound surfactant were derived from the calorimetric titration curves. An increase in temperature from 25 to 45 degrees C had no noticeable effect on these properties, although the shape of the calorimetric titration curves changed drastically. We find that in dilute solution, the interaction of the more hydrophilic EHEC with ionic surfactants resembles that of PEG. Both the calorimetric and viscosity results indicate that SDS interacts with EHEC through both the ethyl and the ethylene oxide groups while the RTAX surfactants predominately interact with the alkyl groups. While the calorimetric results showed the cationic RTAX surfactants to be indifferent to PEO at ambient temperatures and to interact only weakly with the more hydrophilic EHEC, dodecylammonium chloride was found to interact with both polymers.