The effects of solvency on the interfacial behaviour of non-ionic ethylene oxide-containing polymers have been investigated. In particular, ethyl(hydroxyethyl)cellulose (EHEC) and poly(ethylene oxide)-poly(propylene oxide) (PEO-PPO) copolymers were considered. Both these types of polymers adsorb at a variety of interfaces. On worsening the solvency, e.g. by increasing the temperature or adding cosolutes which lower the cloud point of the polymer solution, there is a concomitant tendency to increase the adsorbed amount and decrease the adsorbed layer thickness. The outcome of the competition, however, depends on for example, the relative increase in the adsorbed amount. Thus, if the adsorbed amount increases strongly on worsening the solvency, the contraction of the adsorbed layer may be masked, and the adsorbed layer thickness may increase with increasing temperature. If the adsorbed amount is kept constant, however, the only effect of worsening the solvency is a contraction of the adsorbed layer. The forces between polymer-coated surfaces also display a strong solvency dependence. Thus, under good solvency conditions, the interaction force is monotonically repulsive, whereas in poor solvents, an attractive region appears in the force-distance curve. Finally, the solvency-dependent adsorption and interaction properties of these polymers strongly affect their performance, for example, as steric stabilizers or surface modifiers.