Adsorption isotherms of a nonionic surfactant, viz. a nonylphenol-polyethylene oxide with 20 ethylene oxide units in the chain, NP-EO ({ }{20}), on poly (methyl methacrylate), PMMA, latex have been determined at (10,25,40,60), and (80^{\circ} \mathrm{C}). At all temperatures the isotherms are of the high affinity type, i.e., strong adsorption at low solution concentration reaching a limiting value at higher concentration. The adsorption is strongly temperature dependent and increases with temperature. Thermodynamic analysis reveals that the only factor significantly affecting the temperature dependence of the adsorption of nonionic surfactants of NP-EO ({ }{n}) type is the polyethylene oxide-water interaction. Adsorption measurements can therefore be used as a sensitive probe for this interaction. Two explanations are given for the temperature dependence of the polyethylene oxide-water interaction. The first is that the temperature dependence of this interaction is dominated by water structuring, normally occurring around hydrophobic molecules. The increase in adsorption with temperature is a result of the decreasing water structuring. The second explanation is that the polymer has a higher probability of occupying less favorable conformations as the temperature is increased, thus rendering the polymer less soluble in the water phatse, which in turn increases the adsorption. (1) 1993 Acutconic Press, Inc.