Adsorption isotherms of a nonionic surfactant, viz. a nonylphenol-polyethylene oxide with 20 ethylene oxide units in the chain, NP-EO20, on poly(methyl methacrylate), PMMA, latex have been determined at 10, 25, 40, 60 and 80°C. At all temperatures the isotherms are of 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 increasing with the temperature. Thermo--dynamic analysis reveals that the only factor significantly affecting the temperature dependence of the adsorption of nonionic surfactants of NP-EOn 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 the water structuring, normally occuring 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 phase, which in turn increases the adsorption.